AoC18/day2p1/main.c

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

int compare_char(const void *a, const void *b)
{
    return *(const char *)a - *(const char *)b;
}

char find_reoccurrence(const char *array, const ssize_t len, const int times)
{
    if (!len) return 0;
    if (!times) return 0;

    char current = *array;
    int count = 0;

    for (const char *i = array; i < array + len; i++) {
        if (*i == current) {
            count++;
            continue;
        }
        if (count == times) return current;
        current = *i;
        count = 1;
    }

    return count == times ? current : 0;
}

int main()
{
    char *line = NULL;
    size_t line_len = 0;
    ssize_t len = 0;
    FILE *f = fopen("input", "r");
    if (!f) {
        perror("input");
        return 1;
    }

    int twice = 0;
    int thrice = 0;

    while ((len = getline(&line, &line_len, f)) != -1) {
        while (line[len - 1] == '\n') line[--len] = '\0';
        qsort(line, len, sizeof(char), compare_char);

        if (find_reoccurrence(line, len, 2)) twice++;
        if (find_reoccurrence(line, len, 3)) thrice++;
    }

    printf("%d\n", twice * thrice);

    free(line);
    fclose(f);
    return 0;
}