const int dx[4] = {-1, 0, 1, 0};

const int dy[4] = {0, -1, 0, 1};

class Solution {

int n, m;

void bfs(int x0, int y0, vector<vector<char>>& board, vector<vector<int>>& vis){

queue<pair<int, int>> q;

vis[x0][y0] = 1;

q.push(make_pair(x0, y0));

while(!q.empty()){

int x = q.front().first, y = q.front().second;

q.pop();

for (int i = 0; i < 4; i++){

int xx = x + dx[i];

int yy = y + dy[i];

if (xx >= 0 and xx < n and yy >= 0 and yy < m and board[xx][yy] == 'O' and vis[xx][yy] == 0){

vis[xx][yy] = 1;

q.push(make_pair(xx,yy));

}

}

}

}

void solve(vector<vector<char>>& board) {

n = board.size();

if (n == 0) return;

m = board[0].size();

vector<vector<int>> vis(n, vector<int>(m, 0));

for (int i = 0; i < n; i++) {

if (board[i][0] == 'O' and vis[i][0] == 0)

bfs(i, 0, board, vis);

if (board[i][m-1] == 'O' and vis[i][m-1] == 0)

bfs(i, m-1, board, vis);

}

for (int i = 0; i < m; i++) {

if (board[0][i] == 'O' and vis[0][i] == 0)

bfs(0, i, board, vis);

if (board[n-1][i] == 'O' and vis[n-1][i] == 0)

bfs(n-1, i, board, vis);

}

for (int i = 0; i < n; i++)

for (int j = 0; j < m; j++)

if (board[i][j] == 'O' and vis[i][j] == 0) board[i][j] = 'X';

}

};