题解 | #被围绕的区域#

dfs, 由于和边界值上的"O"相连的都不能被修改,先对边界值相邻的"O"进行状态调整,再修改符合条件的 "O" 的值

#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
# 
# @param board char字符型二维数组 
# @return char字符型二维数组
#
class Solution:
    def surroundedArea(self , board: List[List[str]]) -> List[List[str]]:
        # write code here
        m, n = len(board), len(board[0])
        dirs = [(0, -1), (-1, 0), (0, 1), (1, 0)]
        def dfs(x, y, board):
            board[x][y] = "G"
            for i, j in dirs:
                xi, yi = x + i, y + j
                if 0 <= xi < m and 0 <= yi < n and board[xi][yi] == "O":
                    dfs(xi, yi, board)

        for i in range(n):
            if board[0][i] == "O":
                dfs(0, i, board)
            if board[m - 1][i] == "O":
                dfs(m - 1, i, board)
        
        for i in range(m):
            if board[i][0] == "O":
                dfs(i, 0, board)
            if board[i][n - 1] == "O":
                dfs(i, n - 1, board)
        
        for i in range(m):
            for j in range(n):
                if board[i][j] == "O":
                    board[i][j] = "X"
        
        for i in range(m):
            for j in range(n):
                if board[i][j] == "G":
                    board[i][j] = "O"
        return board