130 Surrounded Regions

from Queue import Queue
class Solution:
    # @param {character[][]} board
    # @return {void} Do not return anything, modify board in-place instead.
    def solve(self, board):
        q = Queue()
        m = len(board)
        if m == 0:
            return
        n = len(board[0])
        for j in range(0, n):
            if board[0][j] == "O":
                q.put([0,j])
                board[0][j] = "V"
            if board[m-1][j] == "O":
                q.put([m-1,j])
                board[m-1][j] = "V"
        for i in range(0, m):
            if board[i][0] == "O":
                q.put([i,0])
                board[i][0] = "V"
            if board[i][n-1] == "O":
                q.put([i,n-1])
                board[i][n-1] = "V"
        while not q.empty():
            [px, py] = q.get()
            for [x,y] in [[px+1, py], [px-1, py], [px, py+1], [px,py-1]]:
                if 0<=x<m and 0<=y<n and board[x][y] == "O":
                    q.put([x,y])
                    board[x][y] = "V"
        for i in range(0, m):
            for j in range(0,n):
                if board[i][j] != "V":
                    board[i][j] = "X"
                else:
                    board[i][j] = "O"