adventofcode2024/day3/c/day3.c

#include <stdio.h>
#include <stdlib.h>
#include <regex.h>

#define INPUT_MAX 1024*1024
#define MAX_MATCHES 3

int main() {
    char *p, *buf, c;

    buf = calloc(INPUT_MAX, sizeof(char));
    p = buf;

    regex_t regex, doit, dont;
    regmatch_t matches[MAX_MATCHES];

    regcomp(&regex, "mul\\(([0-9]{1,3}),([0-9]{1,3})\\)|do\\(\\)|don't\\(\\)", REG_EXTENDED);

    while ((c = getchar()) != EOF) {
        *p++ = c;
    }

    int sum = 0, sum2 = 0;
    int enabled = 1;
    p = buf;
    for (;;) {
        if(regexec(&regex, p, MAX_MATCHES, matches, 0)) {
            break;
        }

        // mul matched
        if (matches[1].rm_so != -1) {
            // There will be 3 matches: 1 for the whole regex and 2 for the capture groups
            int a, b;
            sscanf(p + matches[1].rm_so, "%i", &a);
            sscanf(p + matches[2].rm_so, "%i", &b);

            sum += a * b;
            if (enabled) {
                sum2 += a * b;
            }
        } else {
            if (*(p + matches[0].rm_so + 2) == 'n') {
                enabled = 0;
            } else {
                enabled = 1;
            }
        }

        p += matches[0].rm_eo;
    }

    regfree(&regex);
    free(buf);

    printf("%i\n", sum);
    printf("%i\n", sum2);
}