Leetcode 130. Surrounded Regions

https://leetcode.com/problems/surrounded-regions/

Solution:

# T:O(m*n) S:O(m+n)
class Solution:
    # @param board, a 2D array
    # Capture all regions by modifying the input board in-place.
    # Do not return any value.
    def solve(self, board):
        if not board:
            return
        current = []
        
        for i in xrange(len(board)):
            current.append((i, 0))
            current.append((i, len(board[0]) - 1))
            
        for i in xrange(len(board[0])):
            current.append((0, i))
            current.append((len(board) - 1, i))
            
        while current:
            i, j = current.pop()
            if board[i][j] in ['O', 'V']:
                board[i][j] = 'V'
                for x, y in [(i + 1, j), (i - 1, j), (i, j + 1), (i, j - 1)]:
                    if 0 <= x < len(board) and\
    0 <= y < len(board[0]) and board[x][y] == 'O':
                        board[x][y] = 'V'
                        current.append((x, y))
                        
        for i in xrange(len(board)):
            for j in range(len(board[0])):
                if board[i][j] != 'V':
                    board[i][j] = 'X'
                else:
                    board[i][j] = 'O'

Run Time: 172 ms