aoc/2015/day07/answer02.c

#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;
}