1class Solution {
2    private void dfs(char[][] board, int row, int col, int m, int n) {
3        if (row < 0 || col < 0 || row >= m || col >= n || board[row][col] != 'O') return;
4        board[row][col] = 'A';
5        dfs(board, row - 1, col, m, n);
6        dfs(board, row + 1, col, m, n);
7        dfs(board, row, col - 1, m, n);
8        dfs(board, row, col + 1, m, n);
9    }
10    
11    public void solve(char[][] board) {
12        int m = board.length;
13        if (m == 0) return;
14        int n = board[0].length;
15
16        for (int i = 0; i < m; i++) {
17            if (board[i][0] == 'O') dfs(board, i, 0, m, n);
18            if (board[i][n - 1] == 'O') dfs(board, i, n - 1, m, n);
19        }
20        
21        for (int j = 0; j < n; j++) {
22            if (board[0][j] == 'O') dfs(board, 0, j, m, n);
23            if (board[m - 1][j] == 'O') dfs(board, m - 1, j, m, n);
24        }
25        
26        for (int i = 0; i < m; i++) {
27            for (int j = 0; j < n; j++) {
28                if (board[i][j] == 'O') board[i][j] = 'X';
29                if (board[i][j] == 'A') board[i][j] = 'O';
30            }
31        }
32    }
33}

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';
        }
}