time-2-digit.c

#include <stdio.h>
#include <stdbool.h>
#include <ctype.h>
#include <string.h>

typedef struct {
    char hr1;
    char hr2;
    char delim1;
    char min1;
    char min2;
    char delim2;
    char sec1;
    char sec2;
    char nul;
} time_string_t;

void advance_one_second(time_string_t *t)
{
    if (t->sec2 != '9') {
        t->sec2 += 1;
        return;
    }

    t->sec2 = '0';

    if (t->sec1 != '5') {
        t->sec1 += 1;
        return;
    }

    t->sec1 = '0';

    if (t->min2 != '9') {
        t->min2 += 1;
        return;
    }

    t->min2 = '0';

    if (t->min1 != '5') {
        t->min1 += 1;
        return;
    }

    t->min1 = '0';

    if (t->hr1 == '2' && t->hr2 == '3') {
        t->hr1 = '0';
        t->hr2 = '0';
        return;
    }

    if (t->hr2 != '9') {
        t->hr2 += 1;
        return;
    }

    t->hr2 = '0';
    t->hr1 += 1;
}

bool is_interesting_point(const time_string_t *t)
{
    char digcount[10] = { 0 };
    digcount[t->hr1 - '0'] += 1;
    digcount[t->hr2 - '0'] += 1;
    digcount[t->min1 - '0'] += 1;
    digcount[t->min2 - '0'] += 1;
    digcount[t->sec1 - '0'] += 1;
    digcount[t->sec2 - '0'] += 1;

    int digs = 0;
    for (unsigned int i = 0; i < sizeof digcount; ++i) {
        if (digcount[i] > 0) {
            digs += 1;
        }
    }

    if (digs > 2) {
        return false;
    } else {
        return true;
    }
}

int find_interesting_points(time_string_t t1, time_string_t t2)
{
    advance_one_second(&t2);

    int count = 0;
    do {
        if (is_interesting_point(&t1)) {
            count += 1;
        }

        advance_one_second(&t1);
    } while (memcmp(&t1, &t2, sizeof t1) != 0);

    return count;
}

int main(int argc, char *argv[])
{
    time_string_t t1;
    time_string_t t2;

    if (argc < 3) {
        return 1;
    } else {
        memcpy(&t1, argv[1], sizeof t1);
        memcpy(&t2, argv[2], sizeof t2);

        printf("number of interesting points between %s and %s is %d",
               argv[1], argv[2], find_interesting_points(t1, t2));

        return 0;
    }
}