原題

給定一個二維的矩陣，包含 'X' 和 'O'（字母 O）。

找到所有被 'X' 圍繞的區(qū)域，并將這些區(qū)域里所有的 'O' 用 'X' 填充。

示例:

X X X X
X O O X
X X O X
X O X X

調(diào)用你的函數(shù)后，該二叉樹變?yōu)椋?/p>

X X X X
X X X X
X X X X
X O X X

思路

只有和最外層的‘O’不聯(lián)通的‘O’才會被‘X’替代。使用深度優(yōu)先標記所有和最外層‘O’聯(lián)通的‘O’為‘-’，再遍歷board將剩余的‘O’改寫成‘X’，‘-’改寫成‘O’。

代碼

class Solution(object):
    __row = None
    __col = None
    def solve(self, board):
        """
        :type board: List[List[str]]
        :rtype: void Do not return anything, modify board in-place instead.
        """
        if not board or not board[0]:
            return
        self.__row = len(board)
        self.__col = len(board[0])
        for j in range(self.__row):
            self.dfs(board, j, 0)
            self.dfs(board, j, self.__col-1)
        for i in range(self.__col):
            self.dfs(board, 0, i)
            self.dfs(board, self.__row-1, i)
        for j in range(self.__row):
            for i in range(self.__col):
                if board[j][i] == 'O':
                    board[j][i] = 'X'
                if board[j][i] == '-':
                    board[j][i] = 'O'

    def dfs(self,board, j, i):
        if 0<=i<self.__col and 0<=j<self.__row and board[j][i] == 'O':
            board[j][i] = '-'
            self.dfs(board,j-1,i)
            self.dfs(board,j+1,i)
            self.dfs(board,j,i-1)
            self.dfs(board,j,i+1)
        else:
            return