1391. Check if There is a Valid Path in a Grid

https://leetcode.com/problems/check-if-there-is-a-valid-path-in-a-grid/

Given a m x n grid. Each cell of the grid represents a street. The street of grid[i][j] can be:

• 1 which means a street connecting the left cell and the right cell.

• 2 which means a street connecting the upper cell and the lower cell.

• 3 which means a street connecting the left cell and the lower cell.

• 4 which means a street connecting the right cell and the lower cell.

• 5 which means a street connecting the left cell and the upper cell.

• 6 which means a street connecting the right cell and the upper cell.

You will initially start at the street of the upper-left cell (0,0). A valid path in the grid is a path which starts from the upper left cell (0,0) and ends at the bottom-right cell (m - 1, n - 1). The path should only follow the streets.

Notice that you are not allowed to change any street.

Return true if there is a valid path in the grid or false otherwise.

Example 1:

Input: grid = [[2,4,3],[6,5,2]]
Output: true
Explanation: As shown you can start at cell (0, 0) and visit all the cells of the grid to reach (m - 1, n - 1).

Example 2:

Input: grid = [[1,2,1],[1,2,1]]
Output: false
Explanation: As shown you the street at cell (0, 0) is not connected with any street of any other cell and you will get stuck at cell (0, 0)

Example 3:

Input: grid = [[1,1,2]]
Output: false
Explanation: You will get stuck at cell (0, 1) and you cannot reach cell (0, 2).

Example 4:

Input: grid = [[1,1,1,1,1,1,3]]
Output: true

Example 5:

Input: grid = [[2],[2],[2],[2],[2],[2],[6]]
Output: true

Constraints:

• m == grid.length

• n == grid[i].length

• 1 <= m, n <= 300

• 1 <= grid[i][j] <= 6

给由如图所示拼图组成的地图，问能否从(0, 0)走到(M-1, N-1)。实体图能否到达=>BFS/DFS。将拼图encode成可以走的方向，检查下个点是否可达，可达时再检查能否从下个点回来，如果都能说明下个点和当前点确实是通的。

class Solution:
    def hasValidPath(self, grid: List[List[int]]) -> bool:
        m = len(grid) 
        n = len(grid[0])
        v = [[False] * n for i in range(m)]
        dirs = [[(0, -1), (0, 1)], 
                [(-1, 0), (1, 0)], 
                [(0, -1), (1, 0)],
                [(1, 0), (0, 1)],
                [(-1, 0), (0, -1)],
                [(-1, 0), (0, 1)]]
        q = [(0, 0)]
        v[0][0] = True
        while len(q) != 0:
            t = q[0]
            q.pop(0)
            for _, d in enumerate(dirs[grid[t[0]][t[1]] - 1]):
                r = t[0] + d[0]
                c = t[1] + d[1]
                if r >= 0 and r < m and c >= 0 and c < n and not v[r][c]:
                    for _, nd in enumerate(dirs[grid[r][c] - 1]):
                        if r + nd[0] == t[0] and c + nd[1] == t[1]:
                            q.append((r, c))
                            v[r][c] = True
        return v[m - 1][n - 1]