leetcode 130. Surrounded Regions

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题目链接：leetcode

思路：
广度优先

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import collections
class Solution:
    def solve(self, board):
        """
        :type board: List[List[str]]
        :rtype: void Do not return anything, modify board in-place instead.
        """
        queue = collections.deque()
        for r in range(len(board)):
            for c in range(len(board[0])):
                if (r in [0, len(board)-1] or c in [0, len(board[0])-1]) and board[r][c] == "O":
                    queue.append((r, c))
        while queue:
            #print(queue)
            r, c = queue.popleft()
            if 0<=r<len(board) and 0<=c<len(board[0]) and board[r][c] == "O":
                board[r][c] = "D"
                queue.append((r-1, c)); queue.append((r+1, c))
                queue.append((r, c-1)); queue.append((r, c+1))
        #print(board)
        for r in range(len(board)):
            for c in range(len(board[0])):
                if board[r][c] == "O":
                    board[r][c] = "X"
                elif board[r][c] == "D":
                    board[r][c] = "O"