Advent of Code Day 16 Part 1

part1.c

#include <fcntl.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/stat.h>

#define MAX_NEIGHBORS 8

typedef struct Room
{
    char name[3];
    int flow;
    int num_neighbors;
    int neighbors[8];
} Room;

typedef struct RoomArray
{
    int size;
    Room *data;
} RoomArray;

static int get_index(char *ptr, RoomArray *arr)
{
    for (int i = 0; i < arr->size; i++) {
        Room *cur = arr->data + i;
        if (cur->name[0] == ptr[0] && cur->name[1] == ptr[1]) {
            return i;
        }
    }
    fprintf(stderr, "Failed to find index for %c%c\n", ptr[0], ptr[1]);
    exit(-1);
}

static void parse_input(RoomArray *arr)
{
    int fd = open("sample", O_RDONLY);
    if (fd == -1) {
        perror("open");
        exit(-1);
    }
    struct stat file_info;
    if (fstat(fd, &file_info) == -1) {
        perror("fstat");
        exit(-1);
    }
    char *buffer = malloc(file_info.st_size);
    if (buffer == NULL) {
        fprintf(stderr, "malloc failed\n");
        exit(-1);
    }
    ssize_t bytes = read(fd, buffer, file_info.st_size);
    if (bytes != file_info.st_size) {
        if (bytes == -1) {
            perror("read");
        } else {
            fprintf(stderr, "Read %zu bytes. Expected %zu\n", bytes, file_info.st_size);
        }
        exit(-1);
    }
    close(fd);
    arr->size = 0;
    for (ssize_t i = 0; i < bytes; i++) {
        if (buffer[i] == '\n') {
            arr->size += 1;
        }
    }
    arr->data = malloc(arr->size * sizeof(Room));
    if (arr->data == NULL) {
        fprintf(stderr, "malloc failed\n");
        exit(-1);
    }
    char *ptr = buffer;
    for (int i = 0; i < arr->size; i++) {
        ptr += 6;
        Room *cur = arr->data + i;
        cur->name[0] = *ptr++;
        cur->name[1] = *ptr++;
        cur->name[2] = '\0';
        while (*ptr != '\n') {
            ptr++;
        }
        ptr++;
    }
    ptr = buffer;
    for (int i = 0; i < arr->size; i++) {
        ptr += 23;
        Room *cur = arr->data + i;
        cur->flow = strtol(ptr, &ptr, 10);
        ptr += 24;
        if (*ptr == ' ') {
            ptr++;
        }
        cur->num_neighbors = 0;
        while (1) {
            if (cur->num_neighbors >= MAX_NEIGHBORS) {
                fprintf(stderr, "Too many neighbors\n");
                exit(-1);
            }
            cur->neighbors[cur->num_neighbors] = get_index(ptr, arr);
            cur->num_neighbors += 1;
            ptr += 2;
            if (*ptr == '\n') {
                break;
            }
            ptr += 2;
        }
        ptr++;
    }
    free(buffer);
}

static int get_best(RoomArray *arr, Room *cur, int minutes, int score)
{
    if (minutes == 0) {
        return score;
    }
    minutes--;
    int best = -1;
    for (int i = 0; i < cur->num_neighbors; i++) {
        int test = get_best(arr, arr->data + cur->neighbors[i], minutes, score);
        if (test > best) {
            best = test;
        }
    }
    if (cur->flow > 0) {
        int temp = cur->flow;
        cur->flow = 0;
        int test = get_best(arr, cur, minutes, score + (temp * minutes));
        if (test > best) {
            best = test;
        }
        cur->flow = temp;
    }
    return best;
}

int main(void)
{
    RoomArray arr;
    parse_input(&arr);
    int answer = get_best(&arr, arr.data, 30, 0);
    printf("Answer: %d\n", answer);
    return 0;
}