力扣 130. 被围绕的区域 python AC

并查集

class Solution:
    def solve(self, board):
        row, col = len(board), len(board[0])
        p = row * col
        bcj = [i for i in range(p + 1)]

        def find(x):
            if x != bcj[x]:
                bcj[x] = find(bcj[x])
            return bcj[x]

        def union(x, y):
            a, b = find(x), find(y)
            if a != b:
                bcj[a] = b

        for i in range(row):
            for j in range(col):
                if board[i][j] == 'O':
                    if i == 0 or i == row - 1 or j == 0 or j == col - 1:
                        union(i * col + j, p)
                    else:
                        for k in [(-1, 0), (0, -1), (1, 0), (0, 1)]:
                            ii, jj = i + k[0], j + k[1]
                            if board[ii][jj] == 'O':
                                union(i * col + j, ii * col + jj)
        for i in range(row):
            for j in range(col):
                if find(p) != find(i * col + j):
                    board[i][j] = 'X'

dfs

class Solution:
    def solve(self, board):
        row, col = len(board), len(board[0])
        start = [(i, j) for i in range(row) for j in range(col) if board[i][j] == 'O' and (i == 0 or i == row - 1 or j == 0 or j == col - 1)]
        o = start.copy()

        def dfs(a, b):
            for x, y in [(-1, 0), (0, -1), (1, 0), (0, 1)]:
                aa, bb = a + x, b + y
                if 0 <= aa < row and 0 <= bb < col and board[aa][bb] == 'O' and (aa, bb) not in o:
                    o.append((aa, bb))
                    dfs(aa, bb)

        for i, j in start:
            dfs(i, j)
        for i in range(row):
            for j in range(col):
                if (i, j) not in o:
                    board[i][j] = 'X'