Leetcode130.py

class Solution:
    def solve(self, board: List[List[str]]) -> None:
        """
        Do not return anything, modify board in-place instead.
        """
        if not board or not board[0]:
            return
        row = len(board)
        col = len(board[0])

        def bfs(i, j):
            from collections import deque
            queue = deque()
            queue.appendleft((i, j))
            while queue:
                i, j = queue.pop()
                if 0 <= i < row and 0 <= j < col and board[i][j] == "O":
                    board[i][j] = "B"
                    for x, y in [(-1, 0), (1, 0), (0, -1), (0, 1)]:
                        queue.appendleft((i + x, j + y))

        for j in range(col):
            # 第一行
            if board[0][j] == "O":
                bfs(0, j)
            # 最后一行
            if board[row - 1][j] == "O":
                bfs(row - 1, j)

        for i in range(row):

            if board[i][0] == "O":
                bfs(i, 0)
            if board[i][col - 1] == "O":
                bfs(i, col - 1)

        for i in range(row):
            for j in range(col):
                if board[i][j] == "O":
                    board[i][j] = "X"
                if board[i][j] == "B":
                    board[i][j] = "O"