Advent of Code Day 25

aoc.c

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

int main()
{
    int fd = open("input", O_RDONLY);
    if (fd == -1)
    {
        perror("open");
        return 1;
    }
    struct stat fileInfo;
    if (fstat(fd, &fileInfo) != 0)
    {
        perror("fstat");
        close(fd);
        return 1;
    }
    char *data = malloc(fileInfo.st_size);
    if (data == NULL)
    {
        puts("malloc failed");
        close(fd);
        return 1;
    }
    ssize_t bytesRead = read(fd, data, fileInfo.st_size);
    close(fd);
    if (bytesRead == -1)
    {
        perror("read");
        free(data);
        return 1;
    }
    if (bytesRead != fileInfo.st_size)
    {
        printf("Error: read %lu bytes. %lu expected.\n", bytesRead, fileInfo.st_size);
        free(data);
        return 1;
    }
    int width = 0;
    int height = 0;
    for (ssize_t i = 0; data[i] != '\n'; i++)
    {
        width++;
    }
    for (ssize_t i = 0; i < bytesRead; i++)
    {
        if (data[i] == '\n')
        {
            height++;
        }
    }
    char *grid = malloc(width * height * sizeof(char) * 2);
    if (grid == NULL)
    {
        puts("malloc failed");
        free(data);
        return 1;
    }
    char *readPointer = data;
    char *writePointer = grid;
    for (int y = 0; y < height; y++)
    {
        memcpy(writePointer, readPointer, width * sizeof(char));
        readPointer += width + 1;
        writePointer += width;
    }
    free(data);
    char *grid2 = grid + (width * height);
    memcpy(grid2, grid, width * height * sizeof(char));
    readPointer = grid;
    writePointer = grid2;
    bool moved = true;
    uint64_t steps = 0;
    while(moved)
    {
        moved = false;
        steps++;
        for (int y = 0; y < height; y++)
        {
            for (int x = 0; x < width; x++)
            {
                char *readFrom = &readPointer[(y * width) + x];
                char *writeFrom = &writePointer[(y * width) + x];
                char *readTo;
                char *writeTo;
                if (x < width - 1)
                {
                    readTo = &readPointer[(y * width) + x + 1];
                    writeTo = &writePointer[(y * width) + x + 1];
                }
                else
                {
                    readTo = &readPointer[y * width];
                    writeTo = &writePointer[y * width];
                }
                if (*readFrom == '>' && *readTo == '.')
                {
                    *writeTo = '>';
                    *writeFrom = '.';
                    moved = true;
                }
            }
        }
        memcpy(readPointer, writePointer, width * height * sizeof(char));
        char *temp = readPointer;
        readPointer = writePointer;
        writePointer = temp;
        for (int y = 0; y < height; y++)
        {
            for (int x = 0; x < width; x++)
            {
                char *readFrom = &readPointer[(y * width) + x];
                char *writeFrom = &writePointer[(y * width) + x];
                char *readTo;
                char *writeTo;
                if (y < height - 1)
                {
                    readTo = &readPointer[((y + 1) * width) + x];
                    writeTo = &writePointer[((y + 1) * width) + x];
                }
                else
                {
                    readTo = &readPointer[x];
                    writeTo = &writePointer[x];
                }
                if (*readFrom == 'v' && *readTo == '.')
                {
                    *writeTo = 'v';
                    *writeFrom = '.';
                    moved = true;
                }
            }
        }
        memcpy(readPointer, writePointer, width * height * sizeof(char));
        temp = readPointer;
        readPointer = writePointer;
        writePointer = temp;
    }
    printf("Steps: %lu\n", steps);
    free(grid);
    return 0;
}