leetccode-130-被围绕的区域

class Solution:
    def solve(self, board: List[List[str]]) -> None:
        """
        Do not return anything, modify board in-place instead.
        """
        if not board or len(board)<=2 or len(board[0])<=2:
            return
        row = len(board)
        col = len(board[0])
        def dfs(i,j):
            if i < 0 or j < 0 or i >= row or j >= col or board[i][j] != ‘O‘:
                return
            board[i][j] = ‘#‘
            dfs(i-1,j)
            dfs(i+1,j)
            dfs(i,j+1)
            dfs(i,j-1)
            
        for i in range(row):
            dfs(i,0)
            dfs(i,col-1)
            
        for j in range(col):
            dfs(0,j)
            dfs(row-1,j)
        for i in range(0, row): 
            for j in range(0, col): 
                if board[i][j] == ‘O‘: 
                    board[i][j] = ‘X‘ 
                if board[i][j] == ‘#‘: 
                    board[i][j] = ‘O‘