usaa21/sk1a/maze.c

#include <stdio.h>
#include <string.h>
#include "maze.h"
#include <assert.h>
#include <unistd.h>

#define CHECKED_BIT 16
#define DIRECTION_BITS 15

enum direction {
    NORTH = 8,
    EAST = 4,
    SOUTH = 2,
    WEST = 1,
    NONE = 0
};

int solve_maze(char* maze, int size) {
    if (maze[0] == 'x') {
        return 0;
    }

    char maze2d[size][size];
    for (int y = 0; y < size; y++) {
        for (int x = 0; x < size; x++) {
            maze2d[y][x] = maze[size * y + x] == 'x' ? 'x' : 0;
        }
    }

    int posY = 0, posX = 0;

    while (1) {
        enum direction next_step;

        if (posX + 1 != size && maze2d[posY][posX + 1] != 'x' && !(maze2d[posY][posX + 1] & CHECKED_BIT)) {
            next_step = EAST;
        } else if (posY + 1 != size && maze2d[posY + 1][posX] != 'x' && !(maze2d[posY + 1][posX] & CHECKED_BIT)) {
            next_step = SOUTH;
        } else if (posX - 1 >= 0 && maze2d[posY][posX - 1] != 'x' && !(maze2d[posY][posX - 1] & CHECKED_BIT)) {
            next_step = WEST;
        } else if (posY - 1 >= 0 && maze2d[posY - 1][posX] != 'x' && !(maze2d[posY - 1][posX] & CHECKED_BIT)) {
            next_step = NORTH;
        } else {
            next_step = NONE;
        }

        if (next_step != NONE) {
            maze2d[posY][posX] |= CHECKED_BIT;
            switch (next_step) {
                case EAST:
                    posX += 1;
                    maze2d[posY][posX] |= WEST;
                    break;
                case SOUTH:
                    posY += 1;
                    maze2d[posY][posX] |= NORTH;
                    break;
                case WEST:
                    posX -= 1;
                    maze2d[posY][posX] |= EAST;
                    break;
                case NORTH:
                    posY -= 1;
                    maze2d[posY][posX] |= SOUTH;
                    break;
                default:
                    break;
            }
        } else {
            char came_from = maze2d[posY][posX] & DIRECTION_BITS;
            maze2d[posY][posX] = CHECKED_BIT;
            switch (came_from) {
                case EAST:
                    posX += 1;
                    break;
                case SOUTH:
                    posY += 1;
                    break;
                case WEST:
                    posX -= 1;
                    break;
                case NORTH:
                    posY -= 1;
                    break;
                default:
                    break;
            }
        }

        if (posX == 0 && posY == 0) {
            return 0;
        } else if (posX == size - 1 && posY == size - 1) {
            maze2d[0][0] = '*';

            //cleanup data bits
            for (int i = 0; i < size; i++) {
                for (int j = 0; j < size; j++) {
                    if (maze2d[i][j] == CHECKED_BIT || maze2d[i][j] == 0) {
                        maze2d[i][j] = ' ';
                    } else if (maze2d[i][j] != 'x') {
                        maze2d[i][j] = '*';
                    }
                }
            }

            //cleanup redundant routes
            for (int i = size - 2; i >= 0; i--) {
                for (int j = size - 2; j >= 0; j--) {
                    if (maze2d[i][j] == '*' && maze2d[i + 1][j] == '*' && maze2d[i + 1][j + 1] == '*' && maze2d[i][j + 1] == '*') {
                        maze2d[i + 1][j + 1] = ' ';
                        maze2d[i][j + 1] = ' ';
                    }
                }
            }

            //serialize
            for (int i = 0; i < size; i++) {
                for (int j = 0; j < size; j++) {
                    maze[i * size + j] = maze2d[i][j];
                }
            }

            return 1;
        }
    }
}