class Solution {
public:
    int n,m;
    void dfs(vector<vector<char>>& board,int x,int y)
    {
        if(x<0 || y<0 || x>=n || y>=m || board[x][y] != 'O')
        {
            return ;
        }
        board[x][y] = 'A';
        dfs(board,x,y-1);
        dfs(board,x,y+1);
        dfs(board,x-1,y);
        dfs(board,x+1,y);
    }
    void solve(vector<vector<char>>& board) {
        n = board.size();
        if(n == 0) 
        {
            return ;
        }
        m = board[0].size();
        for(int i=0;i<n;i++)
        {
            dfs(board,i,0);
            dfs(board,i,m-1);
        }
        for(int i=1;i<m-1;i++)
        {
            dfs(board,0,i);
            dfs(board,n-1,i);
        }

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

    }
};