AoC18/day9p1/main.c

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

struct marble {
    struct marble *next;
    struct marble *prev;
    int value;
};

void *xmalloc(size_t size)
{
    void *res = malloc(size);
    if (!res) {
        perror("malloc");
        exit(1);
    }
    return res;
}

void *xcalloc(size_t nmemb, size_t size)
{
    void *res = calloc(nmemb, size);
    if (!res) {
        perror("calloc");
        exit(1);
    }
    return res;
}

int main(int argc, char *argv[])
{
    if (argc <= 2) {
        fprintf(stderr, "Usage: %s <players> <marbles>\n", argv[0]);
        return 1;
    }

    int players = strtol(argv[1], NULL, 0);
    int marbles = strtol(argv[2], NULL, 0);
    if (!players || marbles <= 1) return 1;

    int *scores = xcalloc(players, sizeof(int));
    int player = 0;

    struct marble *current = xmalloc(sizeof(struct marble));
    current->next = current;
    current->prev = current;
    current->value = 0;

    for (int i = 1; i <= marbles; i++) {
        if (i % 23 == 0) {
            scores[player] += i;
            for (int i = 0; i < 7; i++) {
                current = current->prev;
            }
            scores[player] += current->value;
            current->prev->next = current->next;
            current->next->prev = current->prev;

            struct marble *remove = current;
            current = current->next;
            free(remove);
        } else {
            current = current->next;
            struct marble *new = xmalloc(sizeof(struct marble));
            new->next = current->next;
            new->prev = current;
            new->next->prev = new;
            new->prev->next = new;
            new->value = i;
            current = new;
        }

        if (++player >= players) player = 0;
    }

    int highest = 0;
    for (int *score = scores; score < scores + players; score++) {
        if (*score > highest) highest = *score;
    }
    printf("Highest score: %d\n", highest);

    current->prev->next = NULL;
    while (current->next) {
        current = current->next;
        free(current->prev);
    }
    free(current);
    return 0;
}