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| class Solution:
def solve(self, board: List[List[str]]) -> None:
"""
Do not return anything, modify board in-place instead.
"""
m, n = len(board), len(board[0])
def is_valid_pos(x, y, m, n):
if 0 <= x < m and 0 <= y < n and board[x][y] == 'O':
return True
return False
def find_valid_pos(x, y, m, n):
all_pos = []
if is_valid_pos(x-1, y, m, n):
all_pos.append((x-1, y))
if is_valid_pos(x+1, y, m, n):
all_pos.append((x+1, y))
if is_valid_pos(x, y-1, m, n):
all_pos.append((x, y-1))
if is_valid_pos(x, y+1, m, n):
all_pos.append((x, y+1))
return all_pos
def dfs(board, x, y, m, n):
board[x][y] = '|'
for x, y in find_valid_pos(x, y, m, n):
dfs(board, x, y, m, n)
for i in range(m):
if board[i][0] == 'O':
dfs(board, i, 0, m, n)
for i in range(m):
if board[i][n-1] == 'O':
dfs(board, i, n-1, m, n)
for j in range(n):
if board[0][j] == 'O':
dfs(board, 0, j, m, n)
for j in range(n):
if board[m-1][j] == 'O':
dfs(board, m-1, j, m, n)
for i in range(m):
for j in range(n):
if board[i][j] == 'O':
board[i][j] = 'X'
elif board[i][j] == '|':
board[i][j] = 'O'
|