AoC18/day4p1/main.c

#include <stdio.h>

#include <glib.h>

enum action {
    ACTION_BEGIN,
    ACTION_SLEEP,
    ACTION_WAKE
};

struct event {
    unsigned year;
    unsigned month;
    unsigned day;
    unsigned hour;
    unsigned minute;
    enum action action;
    unsigned guard;
};

gint compare_event(gconstpointer a, gconstpointer b)
{
#define _(x) (int)( \
        (x)->year * 12 * 32 * 24 * 60 + \
        (x)->month * 32 * 24 * 60 + \
        (x)->day * 24 * 60 + \
        (x)->hour * 60 + \
        (x)->minute)
    return (_((struct event *)a) - _((struct event *)b));
#undef _
}

GSList *parse_events(const char *fname)
{
    FILE *f = fopen(fname, "r");
    if (!f) {
        perror(fname);
        return NULL;
    }

    GSList *list = NULL;

    char *line = NULL;
    size_t line_len = 0;
    while (getline(&line, &line_len, f) != -1) {
        g_strstrip(line);

        // Find the action text
        char *action = line;
        while (*action && *action++ != '[');
        while (*action && *action++ != ']');
        if (*action) *action++ = '\0';  // Expect a minimum of one space
        if (!*action) {
            fprintf(stderr, "Warning: ignoring '%s': No action found.\n", line);
            continue;
        }
        g_strstrip(action);

        struct event *event = g_malloc0(sizeof(struct event));

        // Haha what is proper parsing
        sscanf(line, "[%u-%u-%u %u:%u]",
                &event->year,
                &event->month,
                &event->day,
                &event->hour,
                &event->minute
        );

        // Basic sanity check
        if (event->month >= 12 ||
                event->day >= 32 ||
                event->hour >= 24 ||
                event->minute >= 60) {
            fprintf(stderr, "Warning: ignoring '%s': Invalid time.\n", line);
            g_free(event);
            continue;
        }

        // Figure out the action
        if (strcmp(action, "falls asleep") == 0) {
            event->action = ACTION_SLEEP;
        } else if (strcmp(action, "wakes up") == 0) {
            event->action = ACTION_WAKE;
        } else {
            sscanf(action, "Guard #%u begins shift", &event->guard);
            if (!event->guard) continue;
        }

        list = g_slist_prepend(list, event);
    }

    free(line);
    fclose(f);

    // We can't do much without information about the guards
    unsigned current_guard = 0;
    list = g_slist_sort(list, compare_event);
    for (GSList *l = list; l; l = l->next) {
        struct event *event = (struct event *)l->data;
        if (event->action == ACTION_BEGIN) {
            current_guard = event->guard;
        } else {
            event->guard = current_guard;
        }
    }

    return list;
}

unsigned find_sleepiest_guard(GSList *events)
{
    // Figure out which guard has slept the most
    // Assumptions:
    // - All sleep/wake hours are 00
    // - Every sleep action is coupled with a wake action from the same guard
    // According to the puzzle these are safe assumptions to make,
    //   and it's not worth my time to do everything "properly" right now.
    GHashTable *table = g_hash_table_new(NULL, NULL);

    unsigned start_time = 0;
    for (GSList *l = events; l; l = l->next) {
        struct event *event = (struct event *)l->data;

        if (event->action == ACTION_SLEEP) {
            start_time = event->minute;
        } else if (event->action == ACTION_WAKE) {
            unsigned time = event->minute - start_time;
            
            unsigned current_time = GPOINTER_TO_UINT(g_hash_table_lookup(table, GUINT_TO_POINTER(event->guard)));
            current_time += time;
            g_hash_table_insert(table, GUINT_TO_POINTER(event->guard), GUINT_TO_POINTER(current_time));
        }
    }

    unsigned sleepiest_guard = 0;
    unsigned sleepiest_guard_time = 0;

    gpointer key, value;
    GHashTableIter iter;
    g_hash_table_iter_init(&iter, table);
    while (g_hash_table_iter_next(&iter, &key, &value)) {
        unsigned guard = GPOINTER_TO_UINT(key);
        unsigned time = GPOINTER_TO_UINT(value);
        printf("Guard #%u: %u minutes\n", guard, time);
        if (time > sleepiest_guard_time) {
            sleepiest_guard = guard;
            sleepiest_guard_time = time;
        }
    }

    g_hash_table_destroy(table);
    return sleepiest_guard;
}

unsigned find_sleepiest_minute(GSList *events, unsigned guard)
{
    // Figure out which is the guard's most slept minute
    // Also assuming all sleep hours are at 12am
    unsigned char slept[60] = {0};

    unsigned start_time = 0;
    for (GSList *l = events; l; l = l->next) {
        struct event *event = (struct event *)l->data;
        if (event->guard != guard) continue;

        if (event->action == ACTION_SLEEP) {
            start_time = event->minute;
        } else if (event->action == ACTION_WAKE) {
            for (unsigned i = start_time; i < event->minute; i++) {
                if (slept[i] >= UCHAR_MAX) continue;
                slept[i]++;
            }
        }
    }

    unsigned slept_minute = 0;
    unsigned slept_minute_count = 0;
    for (unsigned i = 0; i < 60; i++) {
        if (slept[i] > slept_minute_count) {
            slept_minute = i;
            slept_minute_count = slept[i];
        }
    }

    return slept_minute;
}

int main()
{
    GSList *events = parse_events("input");
    for (GSList *l = events; l; l = l->next) {
        struct event *event = (struct event *)l->data;
        printf("[%04u-%02u-%02u %02u:%02u] %u (%u)\n",
                event->year, event->month, event->day,
                event->hour, event->minute,
                event->action, event->guard);
    }

    unsigned sleepiest_guard = find_sleepiest_guard(events);
    printf("Sleepiest guard: %u\n", sleepiest_guard);

    unsigned sleepiest_minute = find_sleepiest_minute(events, sleepiest_guard);
    printf("Most slept minute: %u\n", sleepiest_minute);

    printf("Result hash: %u\n", sleepiest_guard * sleepiest_minute);

    g_slist_free_full(events, g_free);
    return 0;
}