1class Solution:
2    def solve(self, board: List[List[str]]) -> None:
3        def dfs(row, col):
4            if row < 0 or col < 0 or row >= len(board) or col >= len(board[0]) or board[row][col] != 'O':
5                return
6            board[row][col] = 'A'
7            dfs(row - 1, col)
8            dfs(row + 1, col)
9            dfs(row, col - 1)
10            dfs(row, col + 1)
11
12        m, n = len(board), len(board[0])
13        if m == 0:
14            return
15
16        for i in range(m):
17            if board[i][0] == 'O':
18                dfs(i, 0)
19            if board[i][n - 1] == 'O':
20                dfs(i, n - 1)
21
22        for j in range(n):
23            if board[0][j] == 'O':
24                dfs(0, j)
25            if board[m - 1][j] == 'O':
26                dfs(m - 1, j)
27
28        for i in range(m):
29            for j in range(n):
30                if board[i][j] == 'O':
31                    board[i][j] = 'X'
32                elif board[i][j] == 'A':
33                    board[i][j] = 'O'

1#include <vector>
2#include <queue>
using namespace std;

void bfs(vector<vector<char>>& board, int row, int col, int m, int n) {
    queue<pair<int, int>> q;
    q.push({row, col});
    board[row][col] = 'A';

    while (!q.empty()) {
        auto [curRow, curCol] = q.front();
        q.pop();

        int directions[4][2] = {{1, 0}, {-1, 0}, {0, 1}, {0, -1}};
        for (const auto& dir : directions) {
            int newRow = curRow + dir[0];
            int newCol = curCol + dir[1];
            if (newRow >= 0 && newRow < m && newCol >= 0 && newCol < n && board[newRow][newCol] == 'O') {
                board[newRow][newCol] = 'A';
                q.push({newRow, newCol});
            }
        }
    }
}

void solve(vector<vector<char>>& board) {
    int m = board.size();
    if (m == 0) return;
    int n = board[0].size();

    for (int i = 0; i < m; ++i) {
        if (board[i][0] == 'O') bfs(board, i, 0, m, n);
        if (board[i][n - 1] == 'O') bfs(board, i, n - 1, m, n);
    }

    for (int j = 0; j < n; ++j) {
        if (board[0][j] == 'O') bfs(board, 0, j, m, n);
        if (board[m - 1][j] == 'O') bfs(board, m - 1, j, m, n);
    }
    
    for (int i = 0; i < m; ++i)
        for (int j = 0; j < n; ++j) {
            if (board[i][j] == 'O') board[i][j] = 'X';
            if (board[i][j] == 'A') board[i][j] = 'O';
        }
}