leetcode @python 130. Surrounded Regions

题目链接

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

题目原文

Given a 2D board containing 'X' and 'O', capture all regions surrounded by 'X'.

A region is captured by flipping all 'O's into 'X's in that surrounded region.

For example,

X X X X

X O O X

X X O X

X O X X

After running your function, the board should be:

X X X X

X X X X

X X X X

X O X X

题目大意

给出一个铺满O或者X的区域，将被X围住的O都换成X

解题思路

代码

class Solution(object):
def solve(self, board):
"""
:type board: List[List[str]]
:rtype: void Do not return anything, modify board in-place instead.
"""

def fill(x, y):
if x < 0 or x > m - 1 or y < 0 or y > n - 1 or board[x][y] != 'O':
return
queue.append((x, y))
board[x][y] = 'D'

def bfs(x, y):
if board[x][y] == 'O':
fill(x, y)
while queue:
cur = queue.pop(0)
i = cur[0]
j = cur[1]
fill(i + 1, j)
fill(i - 1, j)
fill(i, j + 1)
fill(i, j - 1)

if len(board) == 0:
return
m = len(board)
n = len(board[0])
queue = []

for i in range(n):
bfs(0, i)
bfs(m - 1, i)
for j in range(1, m - 1):
bfs(j, 0)
bfs(j, n - 1)

for i in range(m):
for j in range(n):
if board[i][j] == 'D':
board[i][j] = 'O'
elif board[i][j] == 'O':
board[i][j] = 'X'