maze-ml/maze.py

import numpy as np
import random
from collections import deque

NORTH, SOUTH, EAST, WEST = 0, 1, 2, 3
_DX = [0, 0, 1, -1]   # col delta for N,S,E,W
_DY = [-1, 1, 0, 0]   # row delta
_OPP = [1, 0, 3, 2]   # opposite direction


def generate(rows: int, cols: int, seed: int | None = None) -> np.ndarray:
    rng = random.Random(seed)
    grid = np.full((rows, cols), 0b1111, dtype=np.uint8)
    visited = np.zeros((rows, cols), dtype=bool)

    start_r, start_c = 0, 0
    visited[start_r, start_c] = True
    stack = [(start_r, start_c)]

    while stack:
        row, col = stack[-1]
        directions = [NORTH, SOUTH, EAST, WEST]
        rng.shuffle(directions)

        moved = False
        for d in directions:
            nr = row + _DY[d]
            nc = col + _DX[d]
            if 0 <= nr < rows and 0 <= nc < cols and not visited[nr, nc]:
                # Carve passage: clear wall bit on current cell
                grid[row, col] &= (~(1 << d)) & 0xFF
                # Clear opposite wall bit on neighbour
                grid[nr, nc] &= (~(1 << _OPP[d])) & 0xFF
                visited[nr, nc] = True
                stack.append((nr, nc))
                moved = True
                break

        if not moved:
            stack.pop()

    return grid


def find_short_seed(rows: int, cols: int, max_ratio: float = 6.5, tries: int = 200) -> tuple[int, np.ndarray, np.ndarray]:
    """Return (seed, grid, bfs_dist) with a short goal path.
    Tries up to `tries` seeds, picks the one whose BFS path < rows*cols/max_ratio.
    Falls back to the best found if none qualifies.
    """
    target = int(rows * cols / max_ratio)
    best = None
    for seed in range(tries):
        grid = generate(rows, cols, seed=seed)
        bfs = bfs_distances(grid, rows - 1, cols - 1)
        path_len = int(bfs[0, 0])
        if best is None or path_len < best[0]:
            best = (path_len, seed, grid, bfs)
        if path_len <= target:
            return seed, grid, bfs
    _, seed, grid, bfs = best
    return seed, grid, bfs


def bfs_distances(grid: np.ndarray, goal_row: int, goal_col: int) -> np.ndarray:
    """BFS distance from every cell to (goal_row, goal_col) through passable walls.
    Returns int array shape (rows, cols); unreachable cells = -1.
    """
    rows, cols = grid.shape
    dist = np.full((rows, cols), -1, dtype=np.int32)
    dist[goal_row, goal_col] = 0
    q = deque([(goal_row, goal_col)])
    while q:
        r, c = q.popleft()
        for d in range(4):
            if is_passable(grid, r, c, d):
                nr, nc = r + _DY[d], c + _DX[d]
                if 0 <= nr < rows and 0 <= nc < cols and dist[nr, nc] == -1:
                    dist[nr, nc] = dist[r, c] + 1
                    q.append((nr, nc))
    return dist


def get_walls(grid: np.ndarray, row: int, col: int) -> tuple[bool, bool, bool, bool]:
    cell = int(grid[row, col])
    wall_n = float((cell >> NORTH) & 1)
    wall_s = float((cell >> SOUTH) & 1)
    wall_e = float((cell >> EAST) & 1)
    wall_w = float((cell >> WEST) & 1)
    return (wall_n, wall_s, wall_e, wall_w)


def is_passable(grid: np.ndarray, row: int, col: int, direction: int) -> bool:
    cell = int(grid[row, col])
    return not bool((cell >> direction) & 1)


def render_static(grid: np.ndarray, cfg) -> 'pygame.Surface':
    import pygame

    rows, cols = grid.shape
    cell_size = getattr(cfg, 'cell_size', 32)
    wall_thickness = getattr(cfg, 'wall_thickness', 2)

    width = cols * cell_size
    height = rows * cell_size

    surface = pygame.Surface((width, height))
    surface.fill((15, 15, 20))

    wall_color = (40, 40, 50)
    t = wall_thickness

    for row in range(rows):
        for col in range(cols):
            x = col * cell_size
            y = row * cell_size
            cell = int(grid[row, col])

            # North wall
            if (cell >> NORTH) & 1:
                pygame.draw.rect(surface, wall_color, (x, y, cell_size, t))

            # South wall
            if (cell >> SOUTH) & 1:
                pygame.draw.rect(surface, wall_color, (x, y + cell_size - t, cell_size, t))

            # East wall
            if (cell >> EAST) & 1:
                pygame.draw.rect(surface, wall_color, (x + cell_size - t, y, t, cell_size))

            # West wall
            if (cell >> WEST) & 1:
                pygame.draw.rect(surface, wall_color, (x, y, t, cell_size))

    # Start cell (0, 0): small cyan circle
    start_cx = cell_size // 2
    start_cy = cell_size // 2
    start_radius = max(2, cell_size // 6)
    pygame.draw.circle(surface, (0, 220, 220), (start_cx, start_cy), start_radius)

    # Goal cell (rows-1, cols-1): green filled circle
    goal_x = (cols - 1) * cell_size + cell_size // 2
    goal_y = (rows - 1) * cell_size + cell_size // 2
    goal_radius = max(3, cell_size // 4)
    pygame.draw.circle(surface, (0, 200, 80), (goal_x, goal_y), goal_radius)

    return surface