diff --git a/2015/day01/answer01.c b/2015/day01/answer01.c
new file mode 100644
index 0000000..1f57c0e
--- /dev/null
+++ b/2015/day01/answer01.c
@@ -0,0 +1,31 @@
+#include <stdio.h>
+#include <stdint.h>
+#include <string.h>
+
+int main() {
+	int32_t floor = 0;
+	
+	FILE *file = fopen("input", "r");
+	if (file == NULL) {
+		perror("Error opening file.");
+		return 1;
+	} 
+
+	char buffer[256];
+	while (fgets(buffer, sizeof(buffer), file) != NULL) {
+		uint16_t length = strlen(buffer);
+		for (uint16_t i = 0; i < length; i++) {
+			if (buffer[i] == '(') floor++;
+			else if(buffer[i] == ')') floor--;
+		}
+	}
+	if (ferror(file)) {
+		perror("Error reading from file.");
+		return 1;
+	}
+    fclose(file);
+
+	printf("floor: %i\n", floor);
+
+	return 0;
+}
diff --git a/2015/day01/answer02.c b/2015/day01/answer02.c
new file mode 100644
index 0000000..7a83247
--- /dev/null
+++ b/2015/day01/answer02.c
@@ -0,0 +1,47 @@
+#include <stdio.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <string.h>
+
+int main() {
+	int32_t floor = 0;
+	uint32_t pos = 0;
+
+	FILE *file = fopen("input", "r");
+	if (file == NULL) {
+		perror("Error opening file.");
+		return 1;
+	}
+
+	char buffer[256];
+	bool breakout = false;
+	while (fgets(buffer, sizeof(buffer), file) != NULL) {
+		uint16_t length = strlen(buffer);
+		if (breakout) break;
+		for (uint16_t i = 0; i < length; i++) {
+			if (buffer[i] == '(') { 
+				floor++; 
+				pos++; 
+			}
+			else if (buffer[i] == ')') { 
+				floor--; 
+				pos++; 
+			}
+
+			if (floor == -1) { 
+				breakout = true; 
+				break; 
+			}
+		}
+	}
+	if (ferror(file)) {
+		perror("Error reading form file.");
+		return 1;
+	}
+	fclose(file);
+
+	printf("position: %i\n", pos);
+
+	return 0;
+}
+
diff --git a/2015/day01/input b/2015/day01/input
new file mode 100644
index 0000000..2d4ad8f
--- /dev/null
+++ b/2015/day01/input
@@ -0,0 +1 @@
+()(((()))(()()()((((()(((())(()(()((((((()(()(((())))((()(((()))((())(()((()()()()(((())(((((((())))()()(()(()(())(((((()()()((())(((((()()))))()(())(((())(())((((((())())))(()())))()))))()())()())((()()((()()()()(()((((((((()()())((()()(((((()(((())((())(()))()((((()((((((((())()((()())(())((()))())((((()())(((((((((((()()(((((()(()))())(((()(()))())((()(()())())())(()(((())(())())()()(()(()((()))((()))))((((()(((()))))((((()(()(()())())()(((()((((())((((()(((()()(())()()()())((()((((((()((()()))()((()))()(()()((())))(((()(((()))((()((()(()))(((()()(()(()()()))))()()(((()(((())())))))((()(((())()(()(())((()())))((((())))(()(()(()())()((()())))(((()((()(())()()((()((())(()()((())(())()))()))((()(())()))())(((((((()(()()(()(())())))))))(()((((((())((((())((())())(()()))))()(())(()())()())((())(()))))(()))(()((()))()(()((((((()()()()((((((((()(()(())((()()(()()))(())()())()((())))()))()())(((()))(())()(())()))()((()((()(()()())(())()()()((())())))((()()(()()((()(())()()())(((()(()()))))(())))(()(()())()))()()))))))()))))((((((())))())))(()(())())(()())))))(()))()))))))()((()))))()))))(()(()((()())())(()()))))(((())()))())())())(((()(()()))(())()(())(())((((((()()))))((()(()))))))(()))())(((()()(()))()())()()()())))))))))))))(())(()))(()))((()(())(()())(())())(()())(())()()(()())))()()()))(())())()))())())(())((())))))))(())))(())))))()))))((())(()(((()))))(()))()((()(())))(()())(((((()))()())()()))))()))))()))())(()(()()()))()))))))((()))))))))))()((()))((()(())((())()()(()()))()(()))))()()(()))()))(((())))(())()((())(())(()())()())())))))))())))()((())))()))(()))()()))(((((((()))())(()()))(()()(()))()(()((()())()))))))(((()()()())))(())()))()())(()()))()()))))))))(())))()))()()))))))()))()())))()(())(())))))()(())()()(()()))))())((()))))()))))(()(((((()))))))))())))())()(())()()))))(())))())()()())()()())()(()))))()))()))))))))())))((()))()))()))())))()())()()())))())))(()((())()((()))())))))())()(())((())))))))))))())()())(())())())(()))(()))()))())(()(())())()())()()(()))))(()(())))))))(())))())(())))))))())()()(())())())))(())))))()))()(()())()(()))())())))))()()(()))()))))())))))))))()))))()))))))())()())()()))))()())))())))))))))))()()))))()()(((()))()()(())()))))((()))))(()))(())())))(())()))))))(()))()))))(())())))))()))(()())))))))))))))())))))))))()((()())(()())))))))((()))))(())(())))()(()())())))())())(()()()())))()))))))())))))())()()())))))))))))()()(()))))()())()))((()())(()))))()(()))))))))))()())())(((())(()))))())()))()))()))))))()))))))(()))))()))))()(())))(())))(()))())()()(()()))()))(()()))))))))()))(()))())(()()(()(()())()()))()))))))))(())))))((()()(()))())())))))()))())(()())()()))())))()(()()()()))((())())))())()(()()))()))))))))(()))(())))()))))(()(()())(()))))()())())()))()()))())))))))))))())()))))))()))))))))())))))()))))())(()())))(())()))())())))))()()(()()())(()())))()()))(((()))(()()()))))()))))()))))((())))()((((((()()))))))())))))))))))(((()))))))))))))(())())))))())(()))))))(()))((()))())))()(()((()))()))()))))))))))())()))()(()()))))())))())(())()(()))()))())(()))()))))(()()))()()(())))))()))(())(()(()()))(()()())))))(((()))))))()))))))))))))(())(()))))()())())()()((()()))())))))(()))))())))))))()()()))))))))())))()(((()()))(())))))(((())())))))((()))()(()))(()))))(()())))(()))())))))()))))(())(())))()((()))(())())))()()))()))))))))()))(()()()(()()()(()))())(())()())(((()))(())))))))))(((()())))()()))))))))()(())(()))()((((())(())(()())))()))(((())()()()))((()))(()))())())))())))(()))())()())())(()(())())()()()(())))())(())))(())))(())()))()))(()((()))))))))())(()))))))())(()()))()()))()(()(()())))()()(()((()((((((()))(())))()()()))())()))((()()(()))())((()(()(()))(()()))))()())))()))()())))))))()()((()())(())))()))(()))(())(()))())(()(())))()()))))))(((()(((()()))()(()(())())((()()))()))()))()))()(()()()(()))((()())()(())))()()))(((())()()())(())()((()()()()(()(())(()()))()(((((()())))((())))))(()()()))))(((()(())))()))((()((()(())()(()((())))((()())()(()))(((()())()()(()))(())(((()((()())()((())()())(((()()))((()((())(()))(()())(()()()))((()))(())(()((()()())((()))(())))(())(())(())))(()())))(((((()(()(((((()())((((()(()())(())(()()(((())((()(((()()(((()()((((((())))())(()((((((()(()))()))()()((()((()))))()(()()(()((()()))))))(((((()(((((())()()()(())())))))))()))((()()(())))(())(()()()())))))(()((((())))))))()()(((()(()(()(()(()())()()()(((((((((()()())()(()))((()()()()()(((((((()())()((())()))((((((()(()(()(()())(((()(((((((()(((())(((((((((())(())())()))((()(()))(((()()())(())(()(()()(((()(())()))())))(())((((((())(()()())()()(((()(((())(()(((())(((((((()(((((((((()))(())(()(()(()))))((()))()(())())())((()(()((()()))((()()((()(())(())(()((())(((())(((()()()((((((()()(())((((())()))))(())((()(()((())))(((((()(()()())())((())())))((())((()((()()((((((())(((()()(()())())(()(()))(()(()))())())()(((((((()(((()(())()()((())((()(()()((()(()()(((((((((((())((())((((((())((()((((()(()((((()(((((((())()((()))))())()((()((((()(()(((()((()())))(())())(((()(((())((((((()(((((((((()()(())))(()(((((()((((()())))((()((()((()(()()(((())((((((((((((()(((())(()(((((()))(()()(()()()()()()((())(((((((())(((((())))))())()(()()(()(()(((()()(((((())(()((()((()(((()()((()((((())()))()((((())(())))()())(((())(())(()()((()(((()()((((((((((()()(()())())(((((((((())((((()))()()((((())(()((((()(((())())(((((((((((()((((())))(())(()(((()(((()((())(((((()((()()(()(()()((((((()((((()((()(()((()(()((((((()))))()()(((((()((()(()(())()))(())(((((((()((((()())(()((()((()(()))())))(())((()))))(((((((()()()())(()))(()()((()())()((()((()()()(()(()()))(()())(())(((((()(((((((((((()((()(((()(((((((()()((((((()(((((()(()((()(((((())((((((()))((((())((()()((())(((())()(((((()()(((((()((()(()(((((((()(((((()((()((()((())(())((())(()))()()))(()()(()(()()(((((((()(((()(((())()(((((()((((((()())((((())()((()((()(()()())(()))((((()()((((((()((()(()(()((((()((()((())((((((()(()(())((((((()((((((((((()((())()))()(()(()(((((()()()))((())))()(()((((((((((((((()(((()((((()((())((()((()(((()()(()(((()((())(()()())))()(()(()(((((()()(()(()((((()(((((())()(()(()))(((((()()(((()()(())((((((((((((((())((())(((((((((((())()()()(())()(()(()(((((((((())(((()))(()()())(()((((()(())(((((()())(())((((((((())()((((()((((((())(()((()(())(((()((((()))(((((((((()()))((((()(())()()()(())(()((())((()()))()(((())(((((())((((((()()))(((((((((()((((((())))(((((((()((()(()(())))())(()(()))()(((((()())(()))()(()(())(((()))))())()())))(((((()))())()((()(()))))((()()()((((((()))()()((((((((())((()(()(((()(()((())((()())(()((((())(()(((()()()(()(()()))())())((((((((((())())((()))()((())(())(())))())()(()()(())))())(()))(((()(()()(((()(((())))()(((()(())()((((((())()))()))()((((((()(()(((((()())))()))))())()()(((()(((((())((()()(()((()((()(()(()(())))(()()()()((()(())(((()((()))((((()))())(())))())(()))()()()())()))(((()()())()((())))(())(()()()()(()())((()(()()((((())))((()((()(())((()(()((())()(()()(((()())()()())((()))((())(((()()(())))()()))(((()((())()(((((()())(())((())()())())((((((()(()(((((()))(()(
diff --git a/2015/day01/makefile b/2015/day01/makefile
new file mode 100644
index 0000000..bb225a0
--- /dev/null
+++ b/2015/day01/makefile
@@ -0,0 +1,10 @@
+CC = gcc
+CFLAGS = -std=c99 -Wall -g
+LDFLAGS =
+
+answer01: answer01.c
+	$(CC) answer01.c -o answer01
+
+answer02: answer02.c
+	$(CC) answer02.c -o answer02
+
diff --git a/2015/day02/answer01.c b/2015/day02/answer01.c
new file mode 100644
index 0000000..04b71b6
--- /dev/null
+++ b/2015/day02/answer01.c
@@ -0,0 +1,53 @@
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+
+int32_t compint(const void *a, const void *b) {
+	uint16_t tmp_a = *((uint16_t *)a);
+	uint16_t tmp_b = *((uint16_t *)b);
+
+	if (tmp_a == tmp_b) return 0;
+	else if (tmp_a > tmp_b) return 1;
+	else return -1;
+}
+
+int main() {
+	FILE *file = fopen("input", "r");
+	if (file == NULL) {
+		perror("main: Error opening file.");
+		return 1;
+	}
+
+	uint16_t l, w, h, sa_tmp;
+	uint32_t sa_cum = 0;
+	int8_t buffer[256];
+	while (fgets(buffer, sizeof(buffer), file) != NULL) {
+		if (sscanf(buffer, "%hux%hux%hu", &l, &w, &h) != 3) {
+			perror("main: Error parsing string.");
+			return 1;
+		}
+		else {
+			//calculate surface area
+			sa_tmp = 2*l*w + 2*w*h + 2*l*h;
+
+			//calculate smallest side
+			uint16_t array[3] = {l, w, h};
+			uint16_t n = sizeof(array)/sizeof(array[0]);
+			qsort(array, n, sizeof(array[0]), compint);
+
+			//calculate cumulative surface area
+			sa_cum = sa_cum + sa_tmp + (array[0]*array[1]);
+		}
+	}
+	if (ferror(file)) {
+		perror("main: Error reading from file.");
+		return 1;
+	}
+	fclose(file);
+
+	printf("cumulative surface area: %u\n", sa_cum);
+
+	return 0;
+}
+			
diff --git a/2015/day02/answer02.c b/2015/day02/answer02.c
new file mode 100644
index 0000000..603552e
--- /dev/null
+++ b/2015/day02/answer02.c
@@ -0,0 +1,56 @@
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h> 
+
+int32_t compint(const void *a, const void *b) {
+	uint16_t tmp_a = *((uint16_t *)a);
+	uint16_t tmp_b = *((uint16_t *)b);
+
+	if (tmp_a == tmp_b) return 0;
+	else if (tmp_a > tmp_b) return 1;
+	else return -1;
+}	
+
+int main() {
+	FILE *file = fopen("input", "r");
+	if (file == NULL) {
+		perror("main: Error opening file.");
+		return 1;
+	}
+
+	uint16_t l, w, h, sp_tmp;
+	uint32_t ribbon = 0;
+	int8_t buffer[256];
+	while (fgets(buffer, sizeof(buffer), file) != NULL) {
+		if (sscanf(buffer, "%hux%hux%hu", &l, &w, &h) != 3) {
+			perror("main: Error parsing string.");
+			return 1;
+		}
+		else {
+			//calculate shortest perimeter
+			uint16_t array[3] = {l, w, h};
+			uint16_t n = sizeof(array)/sizeof(array[0]);
+			qsort(array, n, sizeof(array[0]), compint);
+			sp_tmp = 2*array[0] + 2*array[1];
+
+			//calculate cubic volume
+			uint16_t cv = l*w*h;
+
+			//calculate cumulative ribbon length
+			ribbon = ribbon + sp_tmp + cv;
+		}
+	}
+	if (ferror(file)) {
+		perror("main: Error reading from file.");
+		return 1;
+	}
+	fclose(file);
+
+	printf("total ribbon length: %u\n", ribbon);
+
+	return 0;
+}
+
+
+
diff --git a/2015/day02/input b/2015/day02/input
new file mode 100644
index 0000000..908022e
--- /dev/null
+++ b/2015/day02/input
@@ -0,0 +1,1000 @@
+3x11x24
+13x5x19
+1x9x27
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+6x8x17
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+10x9x12
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diff --git a/2015/day02/makefile b/2015/day02/makefile
new file mode 100644
index 0000000..bb225a0
--- /dev/null
+++ b/2015/day02/makefile
@@ -0,0 +1,10 @@
+CC = gcc
+CFLAGS = -std=c99 -Wall -g
+LDFLAGS =
+
+answer01: answer01.c
+	$(CC) answer01.c -o answer01
+
+answer02: answer02.c
+	$(CC) answer02.c -o answer02
+
diff --git a/2015/day03/answer01.c b/2015/day03/answer01.c
new file mode 100644
index 0000000..b62322b
--- /dev/null
+++ b/2015/day03/answer01.c
@@ -0,0 +1,70 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+#include "01_hashtable.c"
+
+house **process_next_house(house **hash_table, uint32_t *table_size, int32_t *x, int32_t *y, uint32_t *hcount) {
+	//first check to see if we need to enlarge the hash table
+	if (hash(*x, *y) > *table_size - 1) {
+		*table_size = *table_size * 2;
+		hash_table = ht_resize(hash_table, *table_size / 2, *table_size);
+	}
+
+	//process next house
+	house *loc = ht_lookup(hash_table, *x, *y);
+	if (loc == NULL) {
+		(*hcount)++;
+		ht_insert(hash_table, *x, *y, 1);
+	} else {
+		(loc->p)++;
+	} 
+
+	return hash_table;
+}
+
+int main() {
+	FILE *file = fopen("input", "r");
+	if (file == NULL) {
+		perror("main: error opening file.");
+		return 1;
+	}
+
+	uint32_t table_size = 25;
+	house **hash_table = ht_init(table_size);
+
+	int32_t x = 0;
+	int32_t y = 0;
+	ht_insert(hash_table, x, y, 1);		//initial house at (0, 0).
+	uint32_t hcount = 1;
+
+	int32_t c;
+	while ((c = fgetc(file)) != EOF) {
+		if(c == '^') {
+			y++;
+			hash_table = process_next_house(hash_table, &table_size, &x, &y, &hcount);
+		} else if (c == 'v') {
+			y--;
+			hash_table = process_next_house(hash_table, &table_size, &x, &y, &hcount);
+		} else if (c == '>') {
+			x++;
+			hash_table = process_next_house(hash_table, &table_size, &x, &y, &hcount);
+		} else if (c == '<') {
+			x--;
+			hash_table = process_next_house(hash_table, &table_size, &x, &y, &hcount);
+		} 
+	}
+	if (ferror(file)) {
+		perror("main: error reading from file.");
+		return -1;
+	}
+	fclose(file);
+
+	printf("unique houses: %u\n", hcount);
+
+	for (uint32_t i = 0; i < table_size; i++) {
+		free(hash_table[i]);
+	}
+	free(hash_table);
+	return 0;
+}
diff --git a/2015/day03/answer02.c b/2015/day03/answer02.c
new file mode 100644
index 0000000..f95373c
--- /dev/null
+++ b/2015/day03/answer02.c
@@ -0,0 +1,104 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+#include "01_hashtable.c"
+
+house **process_next_house(house **hash_table, uint32_t *table_size, int32_t *x, int32_t *y, uint32_t *hcount) {
+	//first check to see if we need to enlarge the hash table
+	if (hash(*x, *y) > *table_size - 1) {
+		*table_size = *table_size * 2;
+		hash_table = ht_resize(hash_table, *table_size / 2, *table_size);
+	}
+
+	//process next house
+	house *loc = ht_lookup(hash_table, *x, *y);
+	if (loc == NULL) {
+		(*hcount)++;
+		ht_insert(hash_table, *x, *y, 1);
+	} else {
+		(loc->p)++;
+	} 
+
+	return hash_table;
+}
+
+int main() {
+	FILE *file = fopen("input", "r");
+	if (file == NULL) {
+		perror("main: error opening file.");
+		return 1;
+	}
+
+	uint32_t table_size = 25;
+	house **hash_table = ht_init(table_size);
+
+    /* Santa */
+	int32_t x_s = 0;
+	int32_t y_s = 0; 
+	ht_insert(hash_table, x_s, y_s, 1);	//initial house at (0, 0)
+	uint32_t hcount = 1;
+
+	/* Robo-Santa */
+	int32_t x_r = 0;
+	int32_t y_r = 0;
+
+	enum toggle {
+		santa,
+		robo_santa
+	};
+	enum toggle turn = robo_santa;
+
+	int32_t c;
+	while ((c = fgetc(file)) != EOF) {
+		turn = turn ^ robo_santa;	//toggle turn
+		switch(turn) {
+			case santa:
+				if (c == '^') {
+					y_s++;
+					hash_table = process_next_house(hash_table, &table_size, &x_s, &y_s, &hcount);
+				} else if (c == 'v') {
+					y_s--;
+					hash_table = process_next_house(hash_table, &table_size, &x_s, &y_s, &hcount);
+				} else if (c == '>') {
+					x_s++;
+					hash_table = process_next_house(hash_table, &table_size, &x_s, &y_s, &hcount);
+				} else if (c == '<') {
+					x_s--;
+					hash_table = process_next_house(hash_table, &table_size, &x_s, &y_s, &hcount);
+				}
+				break;
+			case robo_santa:
+                if (c == '^') {
+					y_r++;
+					hash_table = process_next_house(hash_table, &table_size, &x_r, &y_r, &hcount);
+				} else if (c == 'v') {
+					y_r--;
+					hash_table = process_next_house(hash_table, &table_size, &x_r, &y_r, &hcount);
+				} else if (c == '>') {
+					x_r++;
+					hash_table = process_next_house(hash_table, &table_size, &x_r, &y_r, &hcount);
+				} else if (c == '<') {
+					x_r--;
+					hash_table = process_next_house(hash_table, &table_size, &x_r, &y_r, &hcount);
+				}
+				break; 
+			default:
+				perror("main: turn error.");
+				return -1;
+		}
+	}
+	if (ferror(file)) {
+		perror("main: error reading from file.");
+		return -1;
+	}
+	fclose(file);
+
+	printf("unique houses: %u\n", hcount);
+
+	for (uint32_t i = 0; i < table_size; i++) {
+		free(hash_table[i]);
+	}
+	free(hash_table);
+	return 0;
+}
diff --git a/2015/day03/input b/2015/day03/input
new file mode 100644
index 0000000..f7791cc
--- /dev/null
+++ b/2015/day03/input
@@ -0,0 +1 @@
+v>v<vvv<<vv^v<v>vv>v<<<^^^^^<<^<vv>^>v^>^>^>^>^><vvvv<^>^<<^><<<^vvvv>^>^><^v^><^<>^^>^vvv^<vv>>^>^^<>><>^>vvv>>^vv>^<><>^<v^>^>^><vv^vv^>><<^><<v>><>^<^>>vvv>v>>>v<<^<><^<v<>v>^^v^^^<^v^^>>><^>^>v<>^<>>^>^^v^><v<v>>><>v<v^v>^v<>>^><v>^<>v^>^<>^v^^^v^^>>vv<<^^><^<vvv>^>^^<^>>^^^^^v^<v>vv<>>v^v<^v^^<><^<^vv^><>><><>v>vvv^vv^^<<><<vvv><<^v^><v<>vvv^<^>vvvv^>^>>^v^<v^vv<^^v<>v>vv^<>><v<<<^v^<<><v<^<^<><^^^>^>>v>^>v^<>v><^<^<v^>^^vv<^^<>v^v^vv<>>>>v^v<>><^^v>vv^^>v^v>v<vv>>v>><v^v^v>vv>^^>^v><<vv^v^^vv<^v><^<<v<v^>vv^^^<v^>v>v^^^>><^^<v^<^>>v><vv<v^^>^^v>>v^^^<^^v>^v>><^<^<>>v<<^^vv>^^^v<^<^<v<v^^vv>^vv^>>v^><v>><<<>^vv^<^<>v^^<<<v<^>^><><v^^>>^^^<^vv<^^^>><^^v>^^v^<v^v^>^^<v>^<^v<^<<<<^<v^>v^<^^<>^^>^><<>>^v><>><^<v><^^^>>vv>^><vv>^^^^^v^vvv><><^<^>v>v^v^>^><><^<^><>v<<vv<^>><>^v^^v>^<<<>^v^>^<<v^vv<>v^<v^^vv><<v^<>>>^<v>vv>v>>>^<^>><vv<>>>>v<v>>>^v>v><>>vvv<^^><<^>^>v<^vvvv<v><vv<><^^^v^^^>v^v<>v<^^v>>><>v<v^>>v><v^>>^^<v<<<^<v<><^^v><<v^><<<<^vv<^<>^><vv<<<<^>>>^v>^v>vv>^v<>v>v<v><^>>v>>^>^><^<v^v^>^v<><><^^>^<vvvv^^<>^^^>vv^v^v>^v^^v^^v><v^<^<>><^<v>v>>vv<<v>>vvvv<vv><>>^v^>^>>v^v^<<<vv<><v<<>>>^v<<v>^^vv^><>v>^>v><<<<<<<^>^^v^<<^^>>vvv^<><>><>^^v<<vv><^^v<^^><vv>v^>>>v^v><v^v<^>v^><>v<<>v>^^v><<<<><^v^v>>^<>^<<>^<v<<>>v<<>><^<<<<^v>^<^v>v>vv<v<v<<>^>v<^<<>v^<vvvv^>v>><<v><v<>v>v>>v^vvv^^>>>v^<^<<^^<<<><v>v^<<v<<<>v<^^<><v<v^^<v>^>v>>v<>^>^^>>^v<<>v^^^>>>^vv<^v<v>^>v>^><>v^^<>^^v^^vv^<^>^<<>><<^>^v>>><<<vvvv><<><v<^v^v<vvv^<><<^<vv><v^v^v^>v>v^<vvv^><^><^<vv><>>v^>^^^<>><v^<^^^<>v<<v<^v>>>^>>v^><<>vvv><^>>v><v><>v>>^>v><<><<>^<>^^^vv><v^>v^^>>^>^<^v<v<^^<^vvvv>v<v>^>v^>^><^<vvvv><^><><<v<>v<v^><^<v^>^v^^<<<<^><^^<^><>>^v<<^<<^vv>v>>v<^<^vv>><v<vv>v<v<v>^v<>^>v<>^v<<<v>>^^v>>><vvv>v^>^v^v>^^^v<vvvv>><^>vvv^<vv^^vv><<<>v<>v>^<vvv^<^<v<v<^vv^^>>vv^<^^v^><^^^^^v<^<v<^>>>vv^v^>^<v>^<><v^<^v>>><^v^<<v<<v<>v>^v<v^v>>^^v<<v<v<<>>>vv>>^v>>^<<<<^><<<><^^>>v<>^vvvv>v^^^>^^^>^<vvvv><^^v<v<>v<^v^v<<v^^^v^<v<^v>v^^<>^>^<^v>vv<v^vv<^<<>v><<^><><^^v<<><^^><>^v>^<><<^<^^<<>vv<>^^<<^>><<<>>vvv>^>v^^v^><<^>v>^>^<^<<>v<^>vv^v^v<>vv<<v>vv<vv><^>v^<>^vv^v^<v<^>>>>v^v><^<><<>vv^<vvv^>>vvv^>v>>><^^vv<vvvv>v<^<^>>^^>^^vv>>><^v<>^v^<<>v^^^<v>^>>^<^<v>>^v<^^^<v>^v>^>>v<vv>>^<v^<<>>^>>><v>v^<<^<v>>^<<^^<>v<^v<^<>v^v>^^v<vvvv>^vv>vvv>v^<^>><v^^vv<<<^>vvvv<>>^^<>v^<><>v<^<>v<>^>v<>vv<v^v>>v<v<^<v^^v^vv^vvv><^^>v>><>>^<^^<>>^>^<v^>>vvv^v><v>>^>^>v><><<><vv^v>v<>^v<^vv^^^<>^^<<^^^v<>><v<^<^<^<^^><v^v<^>v^>vvvv>^^v^>^<v<^^^>>^<<vv^<><><^^^^<<>^<><v>vv^<><^>^^<>v^<>>>v><>vvvvv>v>v^^>^<<vvvv<>vv>>v<<^<>^^^v^<><>>^<<<v<v<>>>><><v>v<v<>>^>^^^^vv^^<<><^^<<vv<^<>v>vv<v<><<<^<<v<<<<>v<>>^<^>^>><v>v>><^^<>><<<><<><v^^v<<><^<^v<v^><^^v<<>><<<<^>v^<v>><v^><v<vvv>v^v^<v><<>>v<><<v>^<>><>>^><>v^v>v<<>v<>v^^><<>>>v<<>>>>^>v>><v<<>>>vv>v>^<^^^<>v<v>^<^^v^vvv^>vv>^<v><vvvv>^<<>vvv<<<vv>^^<^>^>>v>v<<<<<>^^vv^>>v>^<^<v^v^>^v>>v>^v<><>^<^>v>v<<<^^^v>^<<<>vvv^v^^>^>>^>v>v<>^^><>>v>^>v<<<^^^v^<v^vv>><><^<^<><vvv<v^>>^v>vv<^v<<^vv>v^<<v>v>v>^v^>^v<<^v^vv>v<v>^<<><v^>>v<>><v<<<^v<<>vvv^<vv<vvv<<>^vv^^v><^>v^vv<<v^<<^^^<^<>^^<<>v<><<v>^><>^<><<v<v^^>vv<>^<v<^<vvv>vv>v><^^v<>><^v^v><><>><v<v>vv<>>><v^^v<>><<^>>><^^^vvv<<<vv<<^v<<<>><<vv>>>>v<<<<<vv><><v>v^^<<^vv^<vv<>>vv>^<>^v^^<>^^^vv>v^^<v<><v>v<v>>^v<v<>>^<v^^><>v^^^>v^^v<vv><^>v^v^<>v>v<v<^^>>v<^^vv^v<^^^^vv<<><<^>>^^<<v^^<<^>v^>>^^^><^^>^v^v>^<<v<vv<<<v<^^^>^>>^v<>^<^>v>^>^v^<^^^<^vv<v><^^>>v<v>^>^v^>>>>^v>^^<<^<v^v<^<<v<<^><^^<v^<><v>v^<<v^^<><<>>><vv<<><>^<>>>v<<v^^^v^^<<<vv<<^<^<^vv^<><><<^^<^^>v^>^<v<>>v^v<><<v>^^v>^<^<vvv<v>v^v>>>^^<^<v^>^vv<<<v<<>^><><^<>v>>>v<v^<>v>><^^^v^^^v<^^<vv^^^>v>v<>>^^<><>v>^<v<>^>>>><>v>^v>^vv^v<vv<<^^>><v<>^>^^<v<^>^<vvv>><>^<<>>><<<><>^^<<<v<>v^>v>v<v>^^^>^>^v<<>v>vv>><<<v>^^<v><vv<<v^^>^>>^><^>v<^<^v>><^^>v<vv^^><><>^><<><>v^>v<><^^>><>^<^^v<^<<v>><v><<<^^<<v<^vv^v<>><>>>^>v<vvv^>^<><v^><^<<^vv<^v^v^v<>v^^v>v^<^>^vv^>>><<>v^vv^<>^v^><<v^v<v>v^<><>>v^v^><>v^vvv^^^<<^<<v<<v<^vv^>>v^v>^^<v<>><>v>>v^<>^>v>^>><<>v^v><^v>v>>><v<v><^<^^>vv<v><^>^<^>^^v><><v<^^v<<><^<<v^<v<<><^^vvv^v>^>^<>>vv>v^^v^^vv<^^>><v^^vv><^v>v^<<v<^v>vvv<>>^v><<>^v<<<>^><^vv><<^^<v^>v<<v>^vv<>^v>>>><<<<^^<^v>^<^^<^<^^>>^^v>^^^^v^^^<<>^^vv<<v^^><v>><^<<><>^>v<>>v^^^>^v^^v^<v^v>v>>>>>^v>^>^^<vvv^^<v^<<<v<<>v>><^^^v<<^^<v>>^<^<^><^<<v^v><<vv<^<>>v>v>^v<><<v>^>vv^v<v>v><^<v>><>^<vv<v^^^^v<^^>><<^^>v>v>^^^<>v>^v^^>vv^vv<^^>><>^>^<>v>><>^v<<v>v>^><^^^v^<vv><<^v^>v^>vv>v^<>v><vv><^v>v<><v^v^v<^v<>^v<v^<<><<v>>^v><v>^^<>vvv^>^<<v^>><^>><^<>^v<v<v<^vvv<><<^v^<v>><<<v>^<^<v>v>^vv^v>v<^^vv<<vvv^<v>><>vv^>v<<>v<vvvv>>v>^^>>><<<^>^vv>><v>^^^>v<^vv<>v<<<v<<<<v>>>>^<^^^^>v<^^<><v>v>v<v^>vv^>v>v<^>^v^<>v>>vvv>^^><^vvv>><>>>^<<^<v<>>>v^^><v<v>>^><>v<^^v^<<v><>^<>>><^v^v>>>^vvvv^<><<<v<^>>v>^v^<v<v<<^<<v^vv^v>v<v<>>v<v^<<<><v^>><^<<^>^^><v>v<^v^<^>v>^<<v>v^<>v^<>vv^<>^>^>v^>^vv<>^^<<>>v<>^v<><v^><><<<vv>v>v^>vv^><<<<v>^v<><>^^<vv>v^^v^^^<v<^^><v^v<>><v<vv>^<>>><vv<^v<<>>^><>>v<v^v^>>>v<<>v<<<<<<<^v<<^^^v<^v<>v^^<<<^<>>v^vv<v>^<^^<^^<<^>vv><^<^^v<<<^><^v<^><>v<vv^>^v^^>>><<vv^^v><^<<^<>>^>>^<<<<v^vv<>>>v>^v>><>v>>v>><>v>><^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diff --git a/2015/day03/makefile b/2015/day03/makefile
new file mode 100644
index 0000000..84520d9
--- /dev/null
+++ b/2015/day03/makefile
@@ -0,0 +1,10 @@
+CC = gcc
+CFLAGS = -std=c99 -Wall -g
+LDFLAGS =
+
+1: answer01.c
+	$(CC) $(CFLAGS) answer01.c -o answer01
+
+2: answer02.c
+	$(CC) $(CFLAGS) answer02.c -o answer02
+
diff --git a/2015/day04/answer01.c b/2015/day04/answer01.c
new file mode 100644
index 0000000..b29c8fa
--- /dev/null
+++ b/2015/day04/answer01.c
@@ -0,0 +1,62 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <openssl/md5.h>
+
+int main() {
+	size_t PUZZLE_SIZE = 8;		//puzzle input is 8 characters with no ending newline character
+
+	//load input string
+	FILE *file = fopen("input", "r");
+	if (file == NULL) {
+		perror("main: error opening file.");
+		return -1;
+	}
+	char input[256];
+	while (fgets(input, sizeof(input), file));
+	if (strlen(input) != PUZZLE_SIZE) {		
+		perror("main: error reading file.");
+		return -1;
+	}
+	printf("puzzle input: %s\n", input);
+	
+	//initialize MD5 context
+	//note: ignore gcc's warnings that MD5 is depreciated
+	MD5_CTX md5_context;
+	uint8_t md5_hash[MD5_DIGEST_LENGTH];
+	char md5_string[MD5_DIGEST_LENGTH * 2 + 1];	//32 hexadecimal digits
+												//each byte needs two characters in hex, plus one for '\0'
+	char *md5_string_ptr = md5_string;
+	
+	int32_t chars_written;
+	int32_t available_space;
+	int32_t count = -1;		//initialize count at -1 so that the first count++ sets it to 0
+ 	
+	while (strncmp(md5_string, "00000", 5) != 0) {
+		count++;
+		chars_written = snprintf(input + PUZZLE_SIZE, sizeof(input) - strlen(input), "%i", count);
+        available_space = sizeof(input) - strlen(input);
+		if (chars_written >= available_space) {
+			perror("main: buffer overflow.");
+			return -1;
+		}
+   	
+		//initialize MD5 context
+		MD5_Init(&md5_context);
+        
+		//update context with input (+ count) data
+		MD5_Update(&md5_context, input, strlen(input));
+
+		//finalize MD5 hash
+		MD5_Final(md5_hash, &md5_context);
+
+	    for (int i = 0; i < MD5_DIGEST_LENGTH; i++) {
+			md5_string_ptr += sprintf(md5_string_ptr, "%02x", md5_hash[i]);
+		}
+		md5_string_ptr = md5_string;	//reset pointer
+	}
+	
+	printf("count %i: %s\n", count, md5_string);
+	return 0;
+}
+
diff --git a/2015/day04/answer02.c b/2015/day04/answer02.c
new file mode 100644
index 0000000..19c25c3
--- /dev/null
+++ b/2015/day04/answer02.c
@@ -0,0 +1,62 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <openssl/md5.h>
+
+int main() {
+	size_t PUZZLE_SIZE = 8;		//puzzle input is 8 characters with no ending newline character
+
+	//load input string
+	FILE *file = fopen("input", "r");
+	if (file == NULL) {
+		perror("main: error opening file.");
+		return -1;
+	}
+	char input[256];
+	while (fgets(input, sizeof(input), file));
+	if (strlen(input) != PUZZLE_SIZE) {		
+		perror("main: error reading file.");
+		return -1;
+	}
+	printf("puzzle input: %s\n", input);
+	
+	//initialize MD5 context
+	//note: ignore gcc's warnings that MD5 is depreciated
+	MD5_CTX md5_context;
+	uint8_t md5_hash[MD5_DIGEST_LENGTH];
+	char md5_string[MD5_DIGEST_LENGTH * 2 + 1];	//32 hexadecimal digits
+												//each byte needs two characters in hex, plus one for '\0'
+	char *md5_string_ptr = md5_string;
+	
+	int32_t chars_written;
+	int32_t available_space;
+	int32_t count = -1;		//initialize count at -1 so that the first count++ sets it to 0
+ 	
+	while (strncmp(md5_string, "000000", 6) != 0) {
+		count++;
+		chars_written = snprintf(input + PUZZLE_SIZE, sizeof(input) - strlen(input), "%i", count);
+        available_space = sizeof(input) - strlen(input);
+		if (chars_written >= available_space) {
+			perror("main: buffer overflow.");
+			return -1;
+		}
+   	
+		//initialize MD5 context
+		MD5_Init(&md5_context);
+        
+		//update context with input (+ count) data
+		MD5_Update(&md5_context, input, strlen(input));
+
+		//finalize MD5 hash
+		MD5_Final(md5_hash, &md5_context);
+
+	    for (int i = 0; i < MD5_DIGEST_LENGTH; i++) {
+			md5_string_ptr += sprintf(md5_string_ptr, "%02x", md5_hash[i]);
+		}
+		md5_string_ptr = md5_string;	//reset pointer
+	}
+	
+	printf("count %i: %s\n", count, md5_string);
+	return 0;
+}
+
diff --git a/2015/day04/input b/2015/day04/input
new file mode 100644
index 0000000..73269d7
--- /dev/null
+++ b/2015/day04/input
@@ -0,0 +1 @@
+ckczppom
\ No newline at end of file
diff --git a/2015/day04/makefile b/2015/day04/makefile
new file mode 100644
index 0000000..f019d54
--- /dev/null
+++ b/2015/day04/makefile
@@ -0,0 +1,10 @@
+CC = gcc
+CFLAGS = -std=c99 -Wall -g
+LDFLAGS = -lcrypto
+
+1: answer01.c
+	$(CC) $(CFLAGS) $(LDFLAGS) answer01.c -o answer01
+
+2: answer02.c
+	$(CC) $(CFLAGS) $(LDFLAGS) answer02.c -o answer02
+
diff --git a/2015/day05/answer01.c b/2015/day05/answer01.c
new file mode 100644
index 0000000..864e066
--- /dev/null
+++ b/2015/day05/answer01.c
@@ -0,0 +1,57 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+
+int main() {
+	//load input string
+	FILE *file = fopen("input", "r");
+	if (file == NULL) {
+		perror("main: error opening file.");
+		return -1;
+	}
+
+	//string exclusions
+	char *ab = "ab";
+	char *cd = "cd";
+	char *pq = "pq";
+	char *xy = "xy";
+
+	uint32_t ncount = 0;
+	uint8_t double_check = 0;
+	uint8_t vowel_check = 0;
+	char input[256];
+	while (fgets(input, sizeof(input), file) != NULL) {
+		//string exclusion test
+		if (strstr(input, ab) || strstr(input, cd) || strstr(input, pq) || strstr(input, xy)) {
+			continue;
+		}
+
+		//double letter test
+		double_check = 0;
+		for (uint8_t i = 0; i < strlen(input); i++) {
+			if (input[i] == input[i+1]) {
+				double_check = 1;
+				break;
+			}
+		}
+
+		//three vowel test
+		vowel_check = 0;
+		for (uint8_t i = 0; i < strlen(input); i++) {
+		    if (input[i] == 'a' || input[i] == 'e' || input[i] == 'i' || input[i] == 'o' || input[i] == 'u')
+				vowel_check++;
+		}
+
+		if (double_check == 1 && vowel_check >= 3)
+			ncount++;
+	}
+	if (ferror(file)) {		
+		perror("main: error reading file.");
+		return -1;
+	}
+
+	printf("ncount: %i\n", ncount);
+	return 0;
+}
+
diff --git a/2015/day05/answer02.c b/2015/day05/answer02.c
new file mode 100644
index 0000000..e6fd352
--- /dev/null
+++ b/2015/day05/answer02.c
@@ -0,0 +1,47 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+
+int main() {
+	//load input string
+	FILE *file = fopen("input", "r");
+	if (file == NULL) {
+		perror("main: error opening file.");
+		return -1;
+	}
+
+	uint32_t ncount = 0;
+	uint8_t two_repeating_check = 0;
+	uint8_t two_separated_check = 0;
+	char input[256];
+	while (fgets(input, sizeof(input), file) != NULL) {
+		
+		//two letters repeating test
+		two_repeating_check = 0;
+		for (uint8_t i = 0; i < strlen(input) - 1; i++) {
+			for (uint8_t j = i + 2; j < strlen(input) - 1; j++) {
+				if (input[i] == input[j] && input[i+1] == input[j+1])
+					two_repeating_check = 1;
+			}
+		}
+
+		//two letters separated by one test
+		two_separated_check = 0;
+		for (uint8_t i = 0; i < strlen(input) - 1; i++) {
+			if (input[i] == input[i+2])
+				two_separated_check = 1;
+		}
+
+		if (two_repeating_check && two_separated_check)
+			ncount++;
+	}
+	if (ferror(file)) {		
+		perror("main: error reading file.");
+		return -1;
+	}
+
+	printf("ncount: %i\n", ncount);
+	return 0;
+}
+
diff --git a/2015/day05/input b/2015/day05/input
new file mode 100644
index 0000000..f3b13a0
--- /dev/null
+++ b/2015/day05/input
@@ -0,0 +1,1000 @@
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diff --git a/2015/day05/makefile b/2015/day05/makefile
new file mode 100644
index 0000000..50e5631
--- /dev/null
+++ b/2015/day05/makefile
@@ -0,0 +1,10 @@
+CC = gcc
+CFLAGS = -std=c99 -Wall -g
+LDFLAGS = 
+
+1: answer01.c
+	$(CC) $(CFLAGS) $(LDFLAGS) answer01.c -o answer01
+
+2: answer02.c
+	$(CC) $(CFLAGS) $(LDFLAGS) answer02.c -o answer02
+
diff --git a/2015/day06/answer01.c b/2015/day06/answer01.c
new file mode 100644
index 0000000..4514ab7
--- /dev/null
+++ b/2015/day06/answer01.c
@@ -0,0 +1,91 @@
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+
+void turn_on(uint16_t grid[1000][1000], uint16_t x, uint16_t y) {
+	grid[x][y] = 1;
+}
+
+void turn_off(uint16_t grid[1000][1000], uint16_t x, uint16_t y) {
+	grid[x][y] = 0;
+}
+
+void toggle(uint16_t grid[1000][1000], uint16_t x, uint16_t y) {
+	if (grid[x][y] == 0)
+		grid[x][y] = 1;
+	else
+		grid[x][y] = 0;
+}
+
+void process_instruction(char *line_buffer, 
+			 char *delimiters,
+			 uint16_t grid[1000][1000],
+			 void (*operation)(uint16_t grid[1000][1000], uint16_t, uint16_t)) {
+	uint16_t x1, x2, y1, y2;
+	char *token;
+
+	token = strtok(NULL, delimiters);
+	x1 = atoi(token);
+	token = strtok(NULL, delimiters);
+	y1 = atoi(token);
+	token = strtok(NULL, delimiters);	//ignore the word "through"
+	token = strtok(NULL, delimiters);
+	x2 = atoi(token);
+	token = strtok(NULL, delimiters);
+	y2 = atoi(token);
+
+	for (uint16_t i = x1; i <= x2; i++)
+		for (uint16_t j = y1; j <= y2; j++)
+			operation(grid, i, j); 
+}
+
+int main() {
+	FILE *file = fopen("input", "r");
+	if (file == NULL) {
+		perror("Error opening file.");
+		return 1;
+	} 
+
+	uint16_t grid[1000][1000] = {0};
+
+	char delimiters[] = " ,";
+	char *token;
+	char line_buffer[256];
+	while (fgets(line_buffer, sizeof(line_buffer), file) != NULL) {
+		token = strtok(line_buffer, delimiters);
+
+		if (!strcmp(token, "toggle")) {
+			process_instruction(line_buffer, delimiters, grid, toggle);
+			continue;
+		}
+
+		if (!strcmp(token, "turn")) {
+			token = strtok(NULL, delimiters);
+			if (!strcmp(token, "on")) {
+				process_instruction(line_buffer, delimiters, grid, turn_on);
+				continue;
+			}
+
+			if (!strcmp(token, "off")) {
+				process_instruction(line_buffer, delimiters, grid, turn_off);
+				continue;
+			}
+		}
+	}
+	if (ferror(file)) {
+		perror("main: Error reading from file.");
+		return 1;
+	}
+	fclose(file);
+
+	uint32_t count = 0;
+	for (uint16_t i = 0; i <= 999; i++)
+		for (uint16_t j = 0; j <= 999; j++)
+			if (grid[i][j] == 1)
+				count++;
+
+	printf("count: %u\n", count);
+
+	return 0;
+}
diff --git a/2015/day06/answer02.c b/2015/day06/answer02.c
new file mode 100644
index 0000000..2778943
--- /dev/null
+++ b/2015/day06/answer02.c
@@ -0,0 +1,88 @@
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+
+void turn_on(float grid[1000][1000], uint16_t x, uint16_t y) {
+	grid[x][y] += 1;
+}
+
+void turn_off(float grid[1000][1000], uint16_t x, uint16_t y) {
+	if (grid[x][y] > 0)
+		grid[x][y] -= 1;
+}
+
+void toggle(float grid[1000][1000], uint16_t x, uint16_t y) {
+	grid[x][y] += 2;
+}
+
+void process_instruction(char *line_buffer, 
+			 char *delimiters,
+			 float grid[1000][1000],
+			 void (*operation)(float grid[1000][1000], uint16_t, uint16_t)) {
+	uint16_t x1, x2, y1, y2;
+	char *token;
+
+	token = strtok(NULL, delimiters);
+	x1 = atoi(token);
+	token = strtok(NULL, delimiters);
+	y1 = atoi(token);
+	token = strtok(NULL, delimiters);	//ignore the word "through"
+	token = strtok(NULL, delimiters);
+	x2 = atoi(token);
+	token = strtok(NULL, delimiters);
+	y2 = atoi(token);
+
+	for (uint16_t x = x1; x <= x2; x++)
+		for (uint16_t y = y1; y <= y2; y++)
+			operation(grid, x, y); 
+}
+
+int main() {
+	FILE *file = fopen("input", "r");
+	if (file == NULL) {
+		perror("Error opening file.");
+		return 1;
+	} 
+ 
+	float grid[1000][1000] = {0};
+
+	char delimiters[] = " ,";
+	char *token;
+	char line_buffer[256];
+	while (fgets(line_buffer, sizeof(line_buffer), file) != NULL) {
+		token = strtok(line_buffer, delimiters);
+
+		if (!strcmp(token, "toggle")) {
+			process_instruction(line_buffer, delimiters, grid, toggle);
+			continue;
+		}
+
+		if (!strcmp(token, "turn")) {
+			token = strtok(NULL, delimiters);
+			if (!strcmp(token, "on")) {
+				process_instruction(line_buffer, delimiters, grid, turn_on);
+				continue;
+			}
+
+			if (!strcmp(token, "off")) {
+				process_instruction(line_buffer, delimiters, grid, turn_off);
+				continue;
+			}
+		}
+	}
+	if (ferror(file)) {
+		perror("main: Error reading from file.");
+		return 1;
+	}
+	fclose(file); 
+
+	uint32_t brightness = 0;
+	for (uint16_t x = 0; x <= 999; x++)
+		for (uint16_t y = 0; y <= 999; y++)
+			brightness += grid[x][y];
+
+	printf("brightness: %u\n", brightness);
+
+	return 0;
+}
diff --git a/2015/day06/input b/2015/day06/input
new file mode 100644
index 0000000..d6cfb3a
--- /dev/null
+++ b/2015/day06/input
@@ -0,0 +1,300 @@
+toggle 461,550 through 564,900
+turn off 370,39 through 425,839
+turn off 464,858 through 833,915
+turn off 812,389 through 865,874
+turn on 599,989 through 806,993
+turn on 376,415 through 768,548
+turn on 606,361 through 892,600
+turn off 448,208 through 645,684
+toggle 50,472 through 452,788
+toggle 205,417 through 703,826
+toggle 533,331 through 906,873
+toggle 857,493 through 989,970
+turn off 631,950 through 894,975
+turn off 387,19 through 720,700
+turn off 511,843 through 581,945
+toggle 514,557 through 662,883
+turn off 269,809 through 876,847
+turn off 149,517 through 716,777
+turn off 994,939 through 998,988
+toggle 467,662 through 555,957
+turn on 952,417 through 954,845
+turn on 565,226 through 944,880
+turn on 214,319 through 805,722
+toggle 532,276 through 636,847
+toggle 619,80 through 689,507
+turn on 390,706 through 884,722
+toggle 17,634 through 537,766
+toggle 706,440 through 834,441
+toggle 318,207 through 499,530
+toggle 698,185 through 830,343
+toggle 566,679 through 744,716
+toggle 347,482 through 959,482
+toggle 39,799 through 981,872
+turn on 583,543 through 846,710
+turn off 367,664 through 595,872
+turn on 805,439 through 964,995
+toggle 209,584 through 513,802
+turn off 106,497 through 266,770
+turn on 975,2 through 984,623
+turn off 316,684 through 369,876
+turn off 30,309 through 259,554
+turn off 399,680 through 861,942
+toggle 227,740 through 850,829
+turn on 386,603 through 552,879
+turn off 703,795 through 791,963
+turn off 573,803 through 996,878
+turn off 993,939 through 997,951
+turn on 809,221 through 869,723
+turn off 38,720 through 682,751
+turn off 318,732 through 720,976
+toggle 88,459 through 392,654
+turn off 865,654 through 911,956
+toggle 264,284 through 857,956
+turn off 281,776 through 610,797
+toggle 492,660 through 647,910
+turn off 879,703 through 925,981
+turn off 772,414 through 974,518
+turn on 694,41 through 755,96
+turn on 452,406 through 885,881
+turn off 107,905 through 497,910
+turn off 647,222 through 910,532
+turn on 679,40 through 845,358
+turn off 144,205 through 556,362
+turn on 871,804 through 962,878
+turn on 545,676 through 545,929
+turn off 316,716 through 413,941
+toggle 488,826 through 755,971
+toggle 957,832 through 976,992
+toggle 857,770 through 905,964
+toggle 319,198 through 787,673
+turn on 832,813 through 863,844
+turn on 818,296 through 818,681
+turn on 71,699 through 91,960
+turn off 838,578 through 967,928
+toggle 440,856 through 507,942
+toggle 121,970 through 151,974
+toggle 391,192 through 659,751
+turn on 78,210 through 681,419
+turn on 324,591 through 593,939
+toggle 159,366 through 249,760
+turn off 617,167 through 954,601
+toggle 484,607 through 733,657
+turn on 587,96 through 888,819
+turn off 680,984 through 941,991
+turn on 800,512 through 968,691
+turn off 123,588 through 853,603
+turn on 1,862 through 507,912
+turn on 699,839 through 973,878
+turn off 848,89 through 887,893
+toggle 344,353 through 462,403
+turn on 780,731 through 841,760
+toggle 693,973 through 847,984
+toggle 989,936 through 996,958
+toggle 168,475 through 206,963
+turn on 742,683 through 769,845
+toggle 768,116 through 987,396
+turn on 190,364 through 617,526
+turn off 470,266 through 530,839
+toggle 122,497 through 969,645
+turn off 492,432 through 827,790
+turn on 505,636 through 957,820
+turn on 295,476 through 698,958
+toggle 63,298 through 202,396
+turn on 157,315 through 412,939
+turn off 69,789 through 134,837
+turn off 678,335 through 896,541
+toggle 140,516 through 842,668
+turn off 697,585 through 712,668
+toggle 507,832 through 578,949
+turn on 678,279 through 886,621
+toggle 449,744 through 826,910
+turn off 835,354 through 921,741
+toggle 924,878 through 985,952
+turn on 666,503 through 922,905
+turn on 947,453 through 961,587
+toggle 525,190 through 795,654
+turn off 62,320 through 896,362
+turn on 21,458 through 972,536
+turn on 446,429 through 821,970
+toggle 376,423 through 805,455
+toggle 494,896 through 715,937
+turn on 583,270 through 667,482
+turn off 183,468 through 280,548
+toggle 623,289 through 750,524
+turn on 836,706 through 967,768
+turn on 419,569 through 912,908
+turn on 428,260 through 660,433
+turn off 683,627 through 916,816
+turn on 447,973 through 866,980
+turn on 688,607 through 938,990
+turn on 245,187 through 597,405
+turn off 558,843 through 841,942
+turn off 325,666 through 713,834
+toggle 672,606 through 814,935
+turn off 161,812 through 490,954
+turn on 950,362 through 985,898
+turn on 143,22 through 205,821
+turn on 89,762 through 607,790
+toggle 234,245 through 827,303
+turn on 65,599 through 764,997
+turn on 232,466 through 965,695
+turn on 739,122 through 975,590
+turn off 206,112 through 940,558
+toggle 690,365 through 988,552
+turn on 907,438 through 977,691
+turn off 838,809 through 944,869
+turn on 222,12 through 541,832
+toggle 337,66 through 669,812
+turn on 732,821 through 897,912
+toggle 182,862 through 638,996
+turn on 955,808 through 983,847
+toggle 346,227 through 841,696
+turn on 983,270 through 989,756
+turn off 874,849 through 876,905
+turn off 7,760 through 678,795
+toggle 973,977 through 995,983
+turn off 911,961 through 914,976
+turn on 913,557 through 952,722
+turn off 607,933 through 939,999
+turn on 226,604 through 517,622
+turn off 3,564 through 344,842
+toggle 340,578 through 428,610
+turn on 248,916 through 687,925
+toggle 650,185 through 955,965
+toggle 831,359 through 933,536
+turn off 544,614 through 896,953
+toggle 648,939 through 975,997
+turn on 464,269 through 710,521
+turn off 643,149 through 791,320
+turn off 875,549 through 972,643
+turn off 953,969 through 971,972
+turn off 236,474 through 772,591
+toggle 313,212 through 489,723
+toggle 896,829 through 897,837
+toggle 544,449 through 995,905
+turn off 278,645 through 977,876
+turn off 887,947 through 946,977
+turn on 342,861 through 725,935
+turn on 636,316 through 692,513
+toggle 857,470 through 950,528
+turn off 736,196 through 826,889
+turn on 17,878 through 850,987
+turn on 142,968 through 169,987
+turn on 46,470 through 912,853
+turn on 182,252 through 279,941
+toggle 261,143 through 969,657
+turn off 69,600 through 518,710
+turn on 372,379 through 779,386
+toggle 867,391 through 911,601
+turn off 174,287 through 900,536
+toggle 951,842 through 993,963
+turn off 626,733 through 985,827
+toggle 622,70 through 666,291
+turn off 980,671 through 985,835
+turn off 477,63 through 910,72
+turn off 779,39 through 940,142
+turn on 986,570 through 997,638
+toggle 842,805 through 943,985
+turn off 890,886 through 976,927
+turn off 893,172 through 897,619
+turn off 198,780 through 835,826
+toggle 202,209 through 219,291
+turn off 193,52 through 833,283
+toggle 414,427 through 987,972
+turn on 375,231 through 668,236
+turn off 646,598 through 869,663
+toggle 271,462 through 414,650
+turn off 679,121 through 845,467
+toggle 76,847 through 504,904
+turn off 15,617 through 509,810
+toggle 248,105 through 312,451
+turn off 126,546 through 922,879
+turn on 531,831 through 903,872
+toggle 602,431 through 892,792
+turn off 795,223 through 892,623
+toggle 167,721 through 533,929
+toggle 813,251 through 998,484
+toggle 64,640 through 752,942
+turn on 155,955 through 892,985
+turn on 251,329 through 996,497
+turn off 341,716 through 462,994
+toggle 760,127 through 829,189
+turn on 86,413 through 408,518
+toggle 340,102 through 918,558
+turn off 441,642 through 751,889
+turn on 785,292 through 845,325
+turn off 123,389 through 725,828
+turn on 905,73 through 983,270
+turn off 807,86 through 879,276
+toggle 500,866 through 864,916
+turn on 809,366 through 828,534
+toggle 219,356 through 720,617
+turn off 320,964 through 769,990
+turn off 903,167 through 936,631
+toggle 300,137 through 333,693
+toggle 5,675 through 755,848
+turn off 852,235 through 946,783
+toggle 355,556 through 941,664
+turn on 810,830 through 867,891
+turn off 509,869 through 667,903
+toggle 769,400 through 873,892
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+toggle 182,380 through 569,552
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+turn off 231,492 through 790,976
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+toggle 911,840 through 990,932
+toggle 547,895 through 667,935
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+turn off 190,902 through 532,970
+turn off 451,530 through 704,613
+toggle 936,774 through 937,775
+turn off 116,843 through 533,934
+turn on 950,906 through 986,993
+turn on 910,51 through 945,989
+turn on 986,498 through 994,945
+turn off 125,324 through 433,704
+turn off 60,313 through 75,728
+turn on 899,494 through 940,947
+toggle 832,316 through 971,817
+toggle 994,983 through 998,984
+toggle 23,353 through 917,845
+toggle 174,799 through 658,859
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+turn off 623,963 through 917,975
+toggle 721,333 through 816,975
+toggle 589,687 through 890,921
+turn on 936,388 through 948,560
+turn off 485,17 through 655,610
+turn on 435,158 through 689,495
+turn on 192,934 through 734,936
+turn off 299,723 through 622,847
+toggle 484,160 through 812,942
+turn off 245,754 through 818,851
+turn on 298,419 through 824,634
+toggle 868,687 through 969,760
+toggle 131,250 through 685,426
+turn off 201,954 through 997,983
+turn on 353,910 through 832,961
+turn off 518,781 through 645,875
+turn off 866,97 through 924,784
+toggle 836,599 through 857,767
+turn on 80,957 through 776,968
+toggle 277,130 through 513,244
+turn off 62,266 through 854,434
+turn on 792,764 through 872,842
+turn off 160,949 through 273,989
+turn off 664,203 through 694,754
+toggle 491,615 through 998,836
+turn off 210,146 through 221,482
+turn off 209,780 through 572,894
+turn on 766,112 through 792,868
+turn on 222,12 through 856,241
diff --git a/2015/day06/makefile b/2015/day06/makefile
new file mode 100644
index 0000000..50e5631
--- /dev/null
+++ b/2015/day06/makefile
@@ -0,0 +1,10 @@
+CC = gcc
+CFLAGS = -std=c99 -Wall -g
+LDFLAGS = 
+
+1: answer01.c
+	$(CC) $(CFLAGS) $(LDFLAGS) answer01.c -o answer01
+
+2: answer02.c
+	$(CC) $(CFLAGS) $(LDFLAGS) answer02.c -o answer02
+
diff --git a/2015/day07/answer01.c b/2015/day07/answer01.c
new file mode 100644
index 0000000..e8a9a76
--- /dev/null
+++ b/2015/day07/answer01.c
@@ -0,0 +1,175 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <string.h>
+#include <ctype.h>
+#include <errno.h>
+#include <limits.h>
+
+typedef enum {
+	ASSIGN,
+	AND,
+	OR,
+	LSHIFT,
+	RSHIFT,
+	NOT
+} Gate;
+
+typedef struct {
+	char l_operand[3];
+	char r_operand[3];
+	Gate gate;
+	bool assigned;
+	uint16_t value;
+} Wire;
+
+/* hash: for single character strings, convert the character to its natural index.
+ * for two character strings, treat the string as a base 26 number. 
+ * e.g., a -> 0, b -> 1, ..., z -> 25, aa -> 26, ..., etc.
+*/
+int32_t hash(char *str) {
+	int32_t length = strlen(str);
+	if (length == 1) {
+		return str[0] - 'a';
+	} else if (length == 2) {
+		return 26 * ((str[0] - 'a') + 1) + (str[1] - 'a');
+	} else {
+		return -1;
+	}
+}
+
+// is_int: return 1 if the string argument is an integer; 0 otherwise.
+int32_t is_int(char *str) {
+    while (isspace((unsigned char)*str)) str++;
+    if (*str == '\0') return 0;
+
+    char *endptr;
+    errno = 0;
+    int64_t val = strtol(str, &endptr, 10);
+    if (endptr == str || ((val == LONG_MIN || val == LONG_MAX) && errno == ERANGE)) {
+        return 0;
+    }
+
+    while (isspace((unsigned char)*endptr)) endptr++;
+    if (*endptr != '\0') return 0;
+
+    return 1;
+}
+
+// get_value: recursively determine the value of the Wire given its name.
+int32_t get_value(Wire *wire, char *wire_name) {
+	if (is_int(wire_name)) {
+		return atoi(wire_name);
+	}
+
+	uint32_t index = hash(wire_name);
+	if (wire[index].assigned == true) {
+		return wire[index].value;
+	}
+
+	uint16_t l_operand, r_operand;
+	if (wire[index].l_operand[0] != '\0')
+		l_operand = get_value(wire, wire[index].l_operand);
+	if (wire[index].r_operand[0] != '\0')
+		r_operand = get_value(wire, wire[index].r_operand);
+
+	switch(wire[index].gate) {
+		case ASSIGN:
+			wire[index].assigned = true;
+			return wire[index].value = r_operand;
+			break;
+		case AND:
+			wire[index].assigned = true;
+			return wire[index].value = l_operand & r_operand;
+			break;
+		case OR:
+			wire[index].assigned = true;
+			return wire[index].value = l_operand | r_operand;
+			break;
+		case LSHIFT:
+			wire[index].assigned = true;
+			return wire[index].value = l_operand << r_operand;
+			break;
+		case RSHIFT:
+			wire[index].assigned = true;
+			return wire[index].value = l_operand >> r_operand;
+			break;
+		case NOT:
+			wire[index].assigned = true;
+			return wire[index].value = ~r_operand;
+			break;
+	}
+
+	//bad gate
+	perror("get_value: bad gate.");
+	return -1;
+}
+
+// process: insert each wire definition (i.e., instruction) into the Wire array.
+void process(Wire *wire, char *left, char *right) {
+	uint32_t index = hash(right);
+
+	if (strstr(left, "AND") != NULL) {
+		sscanf(left, "%s AND %s", wire[index].l_operand, wire[index].r_operand);
+		wire[index].gate = AND;
+	} else if (strstr(left, "OR") != NULL) {
+		sscanf(left, "%s OR %s", wire[index].l_operand, wire[index].r_operand);
+		wire[index].gate = OR;
+	} else if(strstr(left, "LSHIFT") != NULL) {
+		sscanf(left, "%s LSHIFT %s", wire[index].l_operand, wire[index].r_operand);
+		wire[index].gate = LSHIFT;
+	} else if (strstr(left, "RSHIFT") != NULL) {
+		sscanf(left, "%s RSHIFT %s", wire[index].l_operand, wire[index].r_operand);
+		wire[index].gate = RSHIFT;
+	} else if (strstr(left, "NOT") != NULL) {
+		sscanf(left, "NOT %s", wire[index].r_operand);
+		wire[index].gate = NOT;
+	} else if (!is_int(left)) {		//test for definitions like "x -> y"
+		strcpy(wire[index].r_operand, left);
+		uint64_t len = strlen(wire[index].r_operand);
+
+		//remove trailing whitespace
+		for (uint64_t i = len - 1; i >= 0; i--) {
+			if (isspace((unsigned char)wire[index].r_operand[i])) {
+				wire[index].r_operand[i] = '\0';
+			} else {
+				break;
+			}
+		}
+		wire[index].gate = ASSIGN;
+	} else {	//if we end up here, the definition must be like "123 -> x"
+		wire[index].value = atoi(left);
+		wire[index].assigned = true;
+	}
+}
+
+int main() {
+	FILE *file = fopen("input", "r");
+	if (file == NULL) {
+		perror("main: error opening file.");
+		return 1;
+	}
+
+	uint16_t index = 26*26;
+	Wire wire[index];
+	char left[20];	//20 is suffcient to hold the longest possible definition.
+	char right[3];	//3 is sufficient for any one or two character wire name.
+	
+	for (uint16_t i = 0; i < index; i++) {
+		wire[i].l_operand[0] = '\0';
+		wire[i].r_operand[0] = '\0';
+		wire[i].gate = ASSIGN;
+		wire[i].assigned = false;
+		wire[i].value = 0;
+	}
+
+	while (fscanf(file, "%20[a-zA-Z0-9 ] -> %s\n", left, right) != EOF) {
+		process(wire, left, right);
+	}
+	fclose(file);
+
+	printf("a: %hu\n", get_value(wire, "a"));
+
+	return 0;
+}
diff --git a/2015/day07/answer02.c b/2015/day07/answer02.c
new file mode 100644
index 0000000..fef8519
--- /dev/null
+++ b/2015/day07/answer02.c
@@ -0,0 +1,175 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <string.h>
+#include <ctype.h>
+#include <errno.h>
+#include <limits.h>
+
+typedef enum {
+	ASSIGN,
+	AND,
+	OR,
+	LSHIFT,
+	RSHIFT,
+	NOT
+} Gate;
+
+typedef struct {
+	char l_operand[3];
+	char r_operand[3];
+	Gate gate;
+	bool assigned;
+	uint16_t value;
+} Wire;
+
+/* hash: for single character strings, convert the character to its natural index.
+ * for two character strings, treat the string as a base 26 number. 
+ * e.g., a -> 0, b -> 1, ..., z -> 25, aa -> 26, ..., etc.
+*/
+int32_t hash(char *str) {
+	int32_t length = strlen(str);
+	if (length == 1) {
+		return str[0] - 'a';
+	} else if (length == 2) {
+		return 26 * ((str[0] - 'a') + 1) + (str[1] - 'a');
+	} else {
+		return -1;
+	}
+}
+
+// is_int: return 1 if the string argument is an integer; 0 otherwise.
+int32_t is_int(char *str) {
+    while (isspace((unsigned char)*str)) str++;
+    if (*str == '\0') return 0;
+
+    char *endptr;
+    errno = 0;
+    int64_t val = strtol(str, &endptr, 10);
+    if (endptr == str || ((val == LONG_MIN || val == LONG_MAX) && errno == ERANGE)) {
+        return 0;
+    }
+
+    while (isspace((unsigned char)*endptr)) endptr++;
+    if (*endptr != '\0') return 0;
+
+    return 1;
+}
+
+// get_value: recursively determine the value of the Wire given its name.
+int32_t get_value(Wire *wire, char *wire_name) {
+	if (is_int(wire_name)) {
+		return atoi(wire_name);
+	}
+
+	uint32_t index = hash(wire_name);
+	if (wire[index].assigned == true) {
+		return wire[index].value;
+	}
+
+	uint16_t l_operand, r_operand;
+	if (wire[index].l_operand[0] != '\0')
+		l_operand = get_value(wire, wire[index].l_operand);
+	if (wire[index].r_operand[0] != '\0')
+		r_operand = get_value(wire, wire[index].r_operand);
+
+	switch(wire[index].gate) {
+		case ASSIGN:
+			wire[index].assigned = true;
+			return wire[index].value = r_operand;
+			break;
+		case AND:
+			wire[index].assigned = true;
+			return wire[index].value = l_operand & r_operand;
+			break;
+		case OR:
+			wire[index].assigned = true;
+			return wire[index].value = l_operand | r_operand;
+			break;
+		case LSHIFT:
+			wire[index].assigned = true;
+			return wire[index].value = l_operand << r_operand;
+			break;
+		case RSHIFT:
+			wire[index].assigned = true;
+			return wire[index].value = l_operand >> r_operand;
+			break;
+		case NOT:
+			wire[index].assigned = true;
+			return wire[index].value = ~r_operand;
+			break;
+	}
+
+	//bad gate
+	perror("get_value: bad gate.");
+	return -1;
+}
+
+// process: insert each wire definition (i.e., instruction) into the Wire array.
+void process(Wire *wire, char *left, char *right) {
+	uint32_t index = hash(right);
+
+	if (strstr(left, "AND") != NULL) {
+		sscanf(left, "%s AND %s", wire[index].l_operand, wire[index].r_operand);
+		wire[index].gate = AND;
+	} else if (strstr(left, "OR") != NULL) {
+		sscanf(left, "%s OR %s", wire[index].l_operand, wire[index].r_operand);
+		wire[index].gate = OR;
+	} else if(strstr(left, "LSHIFT") != NULL) {
+		sscanf(left, "%s LSHIFT %s", wire[index].l_operand, wire[index].r_operand);
+		wire[index].gate = LSHIFT;
+	} else if (strstr(left, "RSHIFT") != NULL) {
+		sscanf(left, "%s RSHIFT %s", wire[index].l_operand, wire[index].r_operand);
+		wire[index].gate = RSHIFT;
+	} else if (strstr(left, "NOT") != NULL) {
+		sscanf(left, "NOT %s", wire[index].r_operand);
+		wire[index].gate = NOT;
+	} else if (!is_int(left)) {		//test for definitions like "x -> y"
+		strcpy(wire[index].r_operand, left);
+		uint64_t len = strlen(wire[index].r_operand);
+
+		//remove trailing whitespace
+		for (uint64_t i = len - 1; i >= 0; i--) {
+			if (isspace((unsigned char)wire[index].r_operand[i])) {
+				wire[index].r_operand[i] = '\0';
+			} else {
+				break;
+			}
+		}
+		wire[index].gate = ASSIGN;
+	} else {	//if we end up here, the definition must be like "123 -> x"
+		wire[index].value = atoi(left);
+		wire[index].assigned = true;
+	}
+}
+
+int main() {
+	FILE *file = fopen("input2", "r");
+	if (file == NULL) {
+		perror("main: error opening file.");
+		return 1;
+	}
+
+	uint16_t index = 26*26;
+	Wire wire[index];
+	char left[20];	//20 is suffcient to hold the longest possible definition.
+	char right[3];	//3 is sufficient for any one or two character wire name.
+	
+	for (uint16_t i = 0; i < index; i++) {
+		wire[i].l_operand[0] = '\0';
+		wire[i].r_operand[0] = '\0';
+		wire[i].gate = ASSIGN;
+		wire[i].assigned = false;
+		wire[i].value = 0;
+	}
+
+	while (fscanf(file, "%20[a-zA-Z0-9 ] -> %s\n", left, right) != EOF) {
+		process(wire, left, right);
+	}
+	fclose(file);
+
+	printf("a: %hu\n", get_value(wire, "a"));
+
+	return 0;
+}
diff --git a/2015/day07/input b/2015/day07/input
new file mode 100644
index 0000000..56cae92
--- /dev/null
+++ b/2015/day07/input
@@ -0,0 +1,339 @@
+af AND ah -> ai
+NOT lk -> ll
+hz RSHIFT 1 -> is
+NOT go -> gp
+du OR dt -> dv
+x RSHIFT 5 -> aa
+at OR az -> ba
+eo LSHIFT 15 -> es
+ci OR ct -> cu
+b RSHIFT 5 -> f
+fm OR fn -> fo
+NOT ag -> ah
+v OR w -> x
+g AND i -> j
+an LSHIFT 15 -> ar
+1 AND cx -> cy
+jq AND jw -> jy
+iu RSHIFT 5 -> ix
+gl AND gm -> go
+NOT bw -> bx
+jp RSHIFT 3 -> jr
+hg AND hh -> hj
+bv AND bx -> by
+er OR es -> et
+kl OR kr -> ks
+et RSHIFT 1 -> fm
+e AND f -> h
+u LSHIFT 1 -> ao
+he RSHIFT 1 -> hx
+eg AND ei -> ej
+bo AND bu -> bw
+dz OR ef -> eg
+dy RSHIFT 3 -> ea
+gl OR gm -> gn
+da LSHIFT 1 -> du
+au OR av -> aw
+gj OR gu -> gv
+eu OR fa -> fb
+lg OR lm -> ln
+e OR f -> g
+NOT dm -> dn
+NOT l -> m
+aq OR ar -> as
+gj RSHIFT 5 -> gm
+hm AND ho -> hp
+ge LSHIFT 15 -> gi
+jp RSHIFT 1 -> ki
+hg OR hh -> hi
+lc LSHIFT 1 -> lw
+km OR kn -> ko
+eq LSHIFT 1 -> fk
+1 AND am -> an
+gj RSHIFT 1 -> hc
+aj AND al -> am
+gj AND gu -> gw
+ko AND kq -> kr
+ha OR gz -> hb
+bn OR by -> bz
+iv OR jb -> jc
+NOT ac -> ad
+bo OR bu -> bv
+d AND j -> l
+bk LSHIFT 1 -> ce
+de OR dk -> dl
+dd RSHIFT 1 -> dw
+hz AND ik -> im
+NOT jd -> je
+fo RSHIFT 2 -> fp
+hb LSHIFT 1 -> hv
+lf RSHIFT 2 -> lg
+gj RSHIFT 3 -> gl
+ki OR kj -> kk
+NOT ak -> al
+ld OR le -> lf
+ci RSHIFT 3 -> ck
+1 AND cc -> cd
+NOT kx -> ky
+fp OR fv -> fw
+ev AND ew -> ey
+dt LSHIFT 15 -> dx
+NOT ax -> ay
+bp AND bq -> bs
+NOT ii -> ij
+ci AND ct -> cv
+iq OR ip -> ir
+x RSHIFT 2 -> y
+fq OR fr -> fs
+bn RSHIFT 5 -> bq
+0 -> c
+14146 -> b
+d OR j -> k
+z OR aa -> ab
+gf OR ge -> gg
+df OR dg -> dh
+NOT hj -> hk
+NOT di -> dj
+fj LSHIFT 15 -> fn
+lf RSHIFT 1 -> ly
+b AND n -> p
+jq OR jw -> jx
+gn AND gp -> gq
+x RSHIFT 1 -> aq
+ex AND ez -> fa
+NOT fc -> fd
+bj OR bi -> bk
+as RSHIFT 5 -> av
+hu LSHIFT 15 -> hy
+NOT gs -> gt
+fs AND fu -> fv
+dh AND dj -> dk
+bz AND cb -> cc
+dy RSHIFT 1 -> er
+hc OR hd -> he
+fo OR fz -> ga
+t OR s -> u
+b RSHIFT 2 -> d
+NOT jy -> jz
+hz RSHIFT 2 -> ia
+kk AND kv -> kx
+ga AND gc -> gd
+fl LSHIFT 1 -> gf
+bn AND by -> ca
+NOT hr -> hs
+NOT bs -> bt
+lf RSHIFT 3 -> lh
+au AND av -> ax
+1 AND gd -> ge
+jr OR js -> jt
+fw AND fy -> fz
+NOT iz -> ja
+c LSHIFT 1 -> t
+dy RSHIFT 5 -> eb
+bp OR bq -> br
+NOT h -> i
+1 AND ds -> dt
+ab AND ad -> ae
+ap LSHIFT 1 -> bj
+br AND bt -> bu
+NOT ca -> cb
+NOT el -> em
+s LSHIFT 15 -> w
+gk OR gq -> gr
+ff AND fh -> fi
+kf LSHIFT 15 -> kj
+fp AND fv -> fx
+lh OR li -> lj
+bn RSHIFT 3 -> bp
+jp OR ka -> kb
+lw OR lv -> lx
+iy AND ja -> jb
+dy OR ej -> ek
+1 AND bh -> bi
+NOT kt -> ku
+ao OR an -> ap
+ia AND ig -> ii
+NOT ey -> ez
+bn RSHIFT 1 -> cg
+fk OR fj -> fl
+ce OR cd -> cf
+eu AND fa -> fc
+kg OR kf -> kh
+jr AND js -> ju
+iu RSHIFT 3 -> iw
+df AND dg -> di
+dl AND dn -> do
+la LSHIFT 15 -> le
+fo RSHIFT 1 -> gh
+NOT gw -> gx
+NOT gb -> gc
+ir LSHIFT 1 -> jl
+x AND ai -> ak
+he RSHIFT 5 -> hh
+1 AND lu -> lv
+NOT ft -> fu
+gh OR gi -> gj
+lf RSHIFT 5 -> li
+x RSHIFT 3 -> z
+b RSHIFT 3 -> e
+he RSHIFT 2 -> hf
+NOT fx -> fy
+jt AND jv -> jw
+hx OR hy -> hz
+jp AND ka -> kc
+fb AND fd -> fe
+hz OR ik -> il
+ci RSHIFT 1 -> db
+fo AND fz -> gb
+fq AND fr -> ft
+gj RSHIFT 2 -> gk
+cg OR ch -> ci
+cd LSHIFT 15 -> ch
+jm LSHIFT 1 -> kg
+ih AND ij -> ik
+fo RSHIFT 3 -> fq
+fo RSHIFT 5 -> fr
+1 AND fi -> fj
+1 AND kz -> la
+iu AND jf -> jh
+cq AND cs -> ct
+dv LSHIFT 1 -> ep
+hf OR hl -> hm
+km AND kn -> kp
+de AND dk -> dm
+dd RSHIFT 5 -> dg
+NOT lo -> lp
+NOT ju -> jv
+NOT fg -> fh
+cm AND co -> cp
+ea AND eb -> ed
+dd RSHIFT 3 -> df
+gr AND gt -> gu
+ep OR eo -> eq
+cj AND cp -> cr
+lf OR lq -> lr
+gg LSHIFT 1 -> ha
+et RSHIFT 2 -> eu
+NOT jh -> ji
+ek AND em -> en
+jk LSHIFT 15 -> jo
+ia OR ig -> ih
+gv AND gx -> gy
+et AND fe -> fg
+lh AND li -> lk
+1 AND io -> ip
+kb AND kd -> ke
+kk RSHIFT 5 -> kn
+id AND if -> ig
+NOT ls -> lt
+dw OR dx -> dy
+dd AND do -> dq
+lf AND lq -> ls
+NOT kc -> kd
+dy AND ej -> el
+1 AND ke -> kf
+et OR fe -> ff
+hz RSHIFT 5 -> ic
+dd OR do -> dp
+cj OR cp -> cq
+NOT dq -> dr
+kk RSHIFT 1 -> ld
+jg AND ji -> jj
+he OR hp -> hq
+hi AND hk -> hl
+dp AND dr -> ds
+dz AND ef -> eh
+hz RSHIFT 3 -> ib
+db OR dc -> dd
+hw LSHIFT 1 -> iq
+he AND hp -> hr
+NOT cr -> cs
+lg AND lm -> lo
+hv OR hu -> hw
+il AND in -> io
+NOT eh -> ei
+gz LSHIFT 15 -> hd
+gk AND gq -> gs
+1 AND en -> eo
+NOT kp -> kq
+et RSHIFT 5 -> ew
+lj AND ll -> lm
+he RSHIFT 3 -> hg
+et RSHIFT 3 -> ev
+as AND bd -> bf
+cu AND cw -> cx
+jx AND jz -> ka
+b OR n -> o
+be AND bg -> bh
+1 AND ht -> hu
+1 AND gy -> gz
+NOT hn -> ho
+ck OR cl -> cm
+ec AND ee -> ef
+lv LSHIFT 15 -> lz
+ks AND ku -> kv
+NOT ie -> if
+hf AND hl -> hn
+1 AND r -> s
+ib AND ic -> ie
+hq AND hs -> ht
+y AND ae -> ag
+NOT ed -> ee
+bi LSHIFT 15 -> bm
+dy RSHIFT 2 -> dz
+ci RSHIFT 2 -> cj
+NOT bf -> bg
+NOT im -> in
+ev OR ew -> ex
+ib OR ic -> id
+bn RSHIFT 2 -> bo
+dd RSHIFT 2 -> de
+bl OR bm -> bn
+as RSHIFT 1 -> bl
+ea OR eb -> ec
+ln AND lp -> lq
+kk RSHIFT 3 -> km
+is OR it -> iu
+iu RSHIFT 2 -> iv
+as OR bd -> be
+ip LSHIFT 15 -> it
+iw OR ix -> iy
+kk RSHIFT 2 -> kl
+NOT bb -> bc
+ci RSHIFT 5 -> cl
+ly OR lz -> ma
+z AND aa -> ac
+iu RSHIFT 1 -> jn
+cy LSHIFT 15 -> dc
+cf LSHIFT 1 -> cz
+as RSHIFT 3 -> au
+cz OR cy -> da
+kw AND ky -> kz
+lx -> a
+iw AND ix -> iz
+lr AND lt -> lu
+jp RSHIFT 5 -> js
+aw AND ay -> az
+jc AND je -> jf
+lb OR la -> lc
+NOT cn -> co
+kh LSHIFT 1 -> lb
+1 AND jj -> jk
+y OR ae -> af
+ck AND cl -> cn
+kk OR kv -> kw
+NOT cv -> cw
+kl AND kr -> kt
+iu OR jf -> jg
+at AND az -> bb
+jp RSHIFT 2 -> jq
+iv AND jb -> jd
+jn OR jo -> jp
+x OR ai -> aj
+ba AND bc -> bd
+jl OR jk -> jm
+b RSHIFT 1 -> v
+o AND q -> r
+NOT p -> q
+k AND m -> n
+as RSHIFT 2 -> at
diff --git a/2015/day07/input2 b/2015/day07/input2
new file mode 100644
index 0000000..befbd8e
--- /dev/null
+++ b/2015/day07/input2
@@ -0,0 +1,339 @@
+af AND ah -> ai
+NOT lk -> ll
+hz RSHIFT 1 -> is
+NOT go -> gp
+du OR dt -> dv
+x RSHIFT 5 -> aa
+at OR az -> ba
+eo LSHIFT 15 -> es
+ci OR ct -> cu
+b RSHIFT 5 -> f
+fm OR fn -> fo
+NOT ag -> ah
+v OR w -> x
+g AND i -> j
+an LSHIFT 15 -> ar
+1 AND cx -> cy
+jq AND jw -> jy
+iu RSHIFT 5 -> ix
+gl AND gm -> go
+NOT bw -> bx
+jp RSHIFT 3 -> jr
+hg AND hh -> hj
+bv AND bx -> by
+er OR es -> et
+kl OR kr -> ks
+et RSHIFT 1 -> fm
+e AND f -> h
+u LSHIFT 1 -> ao
+he RSHIFT 1 -> hx
+eg AND ei -> ej
+bo AND bu -> bw
+dz OR ef -> eg
+dy RSHIFT 3 -> ea
+gl OR gm -> gn
+da LSHIFT 1 -> du
+au OR av -> aw
+gj OR gu -> gv
+eu OR fa -> fb
+lg OR lm -> ln
+e OR f -> g
+NOT dm -> dn
+NOT l -> m
+aq OR ar -> as
+gj RSHIFT 5 -> gm
+hm AND ho -> hp
+ge LSHIFT 15 -> gi
+jp RSHIFT 1 -> ki
+hg OR hh -> hi
+lc LSHIFT 1 -> lw
+km OR kn -> ko
+eq LSHIFT 1 -> fk
+1 AND am -> an
+gj RSHIFT 1 -> hc
+aj AND al -> am
+gj AND gu -> gw
+ko AND kq -> kr
+ha OR gz -> hb
+bn OR by -> bz
+iv OR jb -> jc
+NOT ac -> ad
+bo OR bu -> bv
+d AND j -> l
+bk LSHIFT 1 -> ce
+de OR dk -> dl
+dd RSHIFT 1 -> dw
+hz AND ik -> im
+NOT jd -> je
+fo RSHIFT 2 -> fp
+hb LSHIFT 1 -> hv
+lf RSHIFT 2 -> lg
+gj RSHIFT 3 -> gl
+ki OR kj -> kk
+NOT ak -> al
+ld OR le -> lf
+ci RSHIFT 3 -> ck
+1 AND cc -> cd
+NOT kx -> ky
+fp OR fv -> fw
+ev AND ew -> ey
+dt LSHIFT 15 -> dx
+NOT ax -> ay
+bp AND bq -> bs
+NOT ii -> ij
+ci AND ct -> cv
+iq OR ip -> ir
+x RSHIFT 2 -> y
+fq OR fr -> fs
+bn RSHIFT 5 -> bq
+0 -> c
+956 -> b
+d OR j -> k
+z OR aa -> ab
+gf OR ge -> gg
+df OR dg -> dh
+NOT hj -> hk
+NOT di -> dj
+fj LSHIFT 15 -> fn
+lf RSHIFT 1 -> ly
+b AND n -> p
+jq OR jw -> jx
+gn AND gp -> gq
+x RSHIFT 1 -> aq
+ex AND ez -> fa
+NOT fc -> fd
+bj OR bi -> bk
+as RSHIFT 5 -> av
+hu LSHIFT 15 -> hy
+NOT gs -> gt
+fs AND fu -> fv
+dh AND dj -> dk
+bz AND cb -> cc
+dy RSHIFT 1 -> er
+hc OR hd -> he
+fo OR fz -> ga
+t OR s -> u
+b RSHIFT 2 -> d
+NOT jy -> jz
+hz RSHIFT 2 -> ia
+kk AND kv -> kx
+ga AND gc -> gd
+fl LSHIFT 1 -> gf
+bn AND by -> ca
+NOT hr -> hs
+NOT bs -> bt
+lf RSHIFT 3 -> lh
+au AND av -> ax
+1 AND gd -> ge
+jr OR js -> jt
+fw AND fy -> fz
+NOT iz -> ja
+c LSHIFT 1 -> t
+dy RSHIFT 5 -> eb
+bp OR bq -> br
+NOT h -> i
+1 AND ds -> dt
+ab AND ad -> ae
+ap LSHIFT 1 -> bj
+br AND bt -> bu
+NOT ca -> cb
+NOT el -> em
+s LSHIFT 15 -> w
+gk OR gq -> gr
+ff AND fh -> fi
+kf LSHIFT 15 -> kj
+fp AND fv -> fx
+lh OR li -> lj
+bn RSHIFT 3 -> bp
+jp OR ka -> kb
+lw OR lv -> lx
+iy AND ja -> jb
+dy OR ej -> ek
+1 AND bh -> bi
+NOT kt -> ku
+ao OR an -> ap
+ia AND ig -> ii
+NOT ey -> ez
+bn RSHIFT 1 -> cg
+fk OR fj -> fl
+ce OR cd -> cf
+eu AND fa -> fc
+kg OR kf -> kh
+jr AND js -> ju
+iu RSHIFT 3 -> iw
+df AND dg -> di
+dl AND dn -> do
+la LSHIFT 15 -> le
+fo RSHIFT 1 -> gh
+NOT gw -> gx
+NOT gb -> gc
+ir LSHIFT 1 -> jl
+x AND ai -> ak
+he RSHIFT 5 -> hh
+1 AND lu -> lv
+NOT ft -> fu
+gh OR gi -> gj
+lf RSHIFT 5 -> li
+x RSHIFT 3 -> z
+b RSHIFT 3 -> e
+he RSHIFT 2 -> hf
+NOT fx -> fy
+jt AND jv -> jw
+hx OR hy -> hz
+jp AND ka -> kc
+fb AND fd -> fe
+hz OR ik -> il
+ci RSHIFT 1 -> db
+fo AND fz -> gb
+fq AND fr -> ft
+gj RSHIFT 2 -> gk
+cg OR ch -> ci
+cd LSHIFT 15 -> ch
+jm LSHIFT 1 -> kg
+ih AND ij -> ik
+fo RSHIFT 3 -> fq
+fo RSHIFT 5 -> fr
+1 AND fi -> fj
+1 AND kz -> la
+iu AND jf -> jh
+cq AND cs -> ct
+dv LSHIFT 1 -> ep
+hf OR hl -> hm
+km AND kn -> kp
+de AND dk -> dm
+dd RSHIFT 5 -> dg
+NOT lo -> lp
+NOT ju -> jv
+NOT fg -> fh
+cm AND co -> cp
+ea AND eb -> ed
+dd RSHIFT 3 -> df
+gr AND gt -> gu
+ep OR eo -> eq
+cj AND cp -> cr
+lf OR lq -> lr
+gg LSHIFT 1 -> ha
+et RSHIFT 2 -> eu
+NOT jh -> ji
+ek AND em -> en
+jk LSHIFT 15 -> jo
+ia OR ig -> ih
+gv AND gx -> gy
+et AND fe -> fg
+lh AND li -> lk
+1 AND io -> ip
+kb AND kd -> ke
+kk RSHIFT 5 -> kn
+id AND if -> ig
+NOT ls -> lt
+dw OR dx -> dy
+dd AND do -> dq
+lf AND lq -> ls
+NOT kc -> kd
+dy AND ej -> el
+1 AND ke -> kf
+et OR fe -> ff
+hz RSHIFT 5 -> ic
+dd OR do -> dp
+cj OR cp -> cq
+NOT dq -> dr
+kk RSHIFT 1 -> ld
+jg AND ji -> jj
+he OR hp -> hq
+hi AND hk -> hl
+dp AND dr -> ds
+dz AND ef -> eh
+hz RSHIFT 3 -> ib
+db OR dc -> dd
+hw LSHIFT 1 -> iq
+he AND hp -> hr
+NOT cr -> cs
+lg AND lm -> lo
+hv OR hu -> hw
+il AND in -> io
+NOT eh -> ei
+gz LSHIFT 15 -> hd
+gk AND gq -> gs
+1 AND en -> eo
+NOT kp -> kq
+et RSHIFT 5 -> ew
+lj AND ll -> lm
+he RSHIFT 3 -> hg
+et RSHIFT 3 -> ev
+as AND bd -> bf
+cu AND cw -> cx
+jx AND jz -> ka
+b OR n -> o
+be AND bg -> bh
+1 AND ht -> hu
+1 AND gy -> gz
+NOT hn -> ho
+ck OR cl -> cm
+ec AND ee -> ef
+lv LSHIFT 15 -> lz
+ks AND ku -> kv
+NOT ie -> if
+hf AND hl -> hn
+1 AND r -> s
+ib AND ic -> ie
+hq AND hs -> ht
+y AND ae -> ag
+NOT ed -> ee
+bi LSHIFT 15 -> bm
+dy RSHIFT 2 -> dz
+ci RSHIFT 2 -> cj
+NOT bf -> bg
+NOT im -> in
+ev OR ew -> ex
+ib OR ic -> id
+bn RSHIFT 2 -> bo
+dd RSHIFT 2 -> de
+bl OR bm -> bn
+as RSHIFT 1 -> bl
+ea OR eb -> ec
+ln AND lp -> lq
+kk RSHIFT 3 -> km
+is OR it -> iu
+iu RSHIFT 2 -> iv
+as OR bd -> be
+ip LSHIFT 15 -> it
+iw OR ix -> iy
+kk RSHIFT 2 -> kl
+NOT bb -> bc
+ci RSHIFT 5 -> cl
+ly OR lz -> ma
+z AND aa -> ac
+iu RSHIFT 1 -> jn
+cy LSHIFT 15 -> dc
+cf LSHIFT 1 -> cz
+as RSHIFT 3 -> au
+cz OR cy -> da
+kw AND ky -> kz
+lx -> a
+iw AND ix -> iz
+lr AND lt -> lu
+jp RSHIFT 5 -> js
+aw AND ay -> az
+jc AND je -> jf
+lb OR la -> lc
+NOT cn -> co
+kh LSHIFT 1 -> lb
+1 AND jj -> jk
+y OR ae -> af
+ck AND cl -> cn
+kk OR kv -> kw
+NOT cv -> cw
+kl AND kr -> kt
+iu OR jf -> jg
+at AND az -> bb
+jp RSHIFT 2 -> jq
+iv AND jb -> jd
+jn OR jo -> jp
+x OR ai -> aj
+ba AND bc -> bd
+jl OR jk -> jm
+b RSHIFT 1 -> v
+o AND q -> r
+NOT p -> q
+k AND m -> n
+as RSHIFT 2 -> at
diff --git a/2015/day07/makefile b/2015/day07/makefile
new file mode 100644
index 0000000..ebf97ea
--- /dev/null
+++ b/2015/day07/makefile
@@ -0,0 +1,16 @@
+CC = gcc
+CFLAGS = -std=c99 -Wall -Wextra
+LDFLAGS = 
+DFLAGS = -std=c99 -Wall -Wextra -g
+
+1: answer01.c
+	$(CC) $(CFLAGS) $(LDFLAGS) answer01.c -o answer01
+
+2: answer02.c
+	$(CC) $(CFLAGS) $(LDFLAGS) answer02.c -o answer02
+
+1d: answer01.c
+	$(CC) $(DFLAGS) $(LDFLAGS) answer01.c -o answer01
+
+2d: answer02.c
+	$(CC) $(DFLAGS) $(LDFLAGS) answer02.c -o answer02