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dfs_130_surroundArea.py
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dfs_130_surroundArea.py
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""" 被围绕的区域
给定一个二维的矩阵,包含 'X' 和 'O'(字母 O)。
找到所有被 'X' 围绕的区域,并将这些区域里所有的 'O' 用 'X' 填充。
思路:
从四方边界 flood,flood的记为‘A’
最后再遍历数组来恢复
比较难想到的是,四方边界起始的flood搜索。
"""
import pdb
class Solution:
def solve(self, board):
"""
input| board: List[List[str]]
Do not return anything, modify board in-place instead
"""
if len(board) == 0:
return
m, n = len(board), len(board[0]) # m row, n col
def dfs(board, i, j):
# terminate
if i < 0 or i >=m or j < 0 or j >=n or board[i][j] != 'O':
# out of range
return
# pre order mark
board[i][j] = 'A'
dfs(board, i+1, j)
dfs(board, i-1, j)
dfs(board, i, j+1)
dfs(board, i, j-1)
for i in range(m):
dfs(board, i, 0)
dfs(board, i, n-1)
for j in range(n):
dfs(board, 0, j)
dfs(board, m-1, j)
for i in range(m):
for j in range(n):
if board[i][j] == 'O':
board[i][j] = 'X'
if board[i][j] == 'A':
board[i][j] = 'O'
if __name__ == "__main__":
board = [["O","X","X","O","X"],["X","O","O","X","O"],["X","O","X","O","X"],["O","X","O","O","O"],["X","X","O","X","O"]]
app = Solution()
app.solve(board)
print(board)