grid.py

import random

FREE     = 0
OBSTACLE = 1
START    = 2
GOAL     = 3


class Grid:
    def __init__(self, rows=10, cols=10, obstacle_ratio=0.2,
                 start=(0, 0), goal=(9, 9), seed=None):
        self.rows  = rows
        self.cols  = cols
        self.start = start
        self.goal  = goal
        self.cells = [[FREE] * cols for _ in range(rows)]
        self._place_endpoints()
        self._generate_obstacles(obstacle_ratio, seed)

    def _place_endpoints(self):
        r0, c0 = self.start
        r1, c1 = self.goal
        self.cells[r0][c0] = START
        self.cells[r1][c1] = GOAL

    def _generate_obstacles(self, ratio, seed):
        if seed is not None:
            random.seed(seed)
        count   = int(self.rows * self.cols * ratio)
        placed  = 0
        blocked = {self.start, self.goal}
        while placed < count:
            r = random.randint(0, self.rows - 1)
            c = random.randint(0, self.cols - 1)
            if (r, c) not in blocked and self.cells[r][c] == FREE:
                self.cells[r][c] = OBSTACLE
                placed += 1

    # ── helpers ──────────────────────────────────────────────
    def in_bounds(self, r, c):
        return 0 <= r < self.rows and 0 <= c < self.cols

    def is_obstacle(self, r, c):
        return self.cells[r][c] == OBSTACLE

    def get_neighbors(self, r, c):
        for dr, dc in [(-1, 0), (1, 0), (0, -1), (0, 1)]:
            nr, nc = r + dr, c + dc
            if self.in_bounds(nr, nc) and not self.is_obstacle(nr, nc):
                yield (nr, nc)