class Solution {

public:

    vector<vector<string>> glo_ans;

    void solve(vector<string> board, int row, int &col_check , int &diag_check

               , int &rdiag_check)

    {

        if(row == board.size())

        {   glo_ans.push_back(board);

            return;

        }

        for(int col =0;col<board[0].size();col++){

                if(board[row][col]=='.')

                {

                    if(((col_check & 1 << col) ==0) && ((diag_check & (1 << (row+col)))==0)

                        && (rdiag_check & (1<<(row-col+board.size()-1))) ==0 )

                    {

                        col_check ^= (1 << col);

                        diag_check ^= (1 << (row+col));

                        rdiag_check ^= (1<<(row-col+board.size()-1));

                        board[row][col]='Q';

                        solve(board , row+1 , col_check, diag_check , rdiag_check);

                        col_check ^= (1 << col);

                        diag_check ^= (1 << (row+col));

                        rdiag_check ^= (1<<(row-col+board.size()-1));

                        board[row][col]='.';

                    }

                }

        }

    }

    vector<vector<string>> solveNQueens(int n) {

        string k = "";

        for(int i =0;i<n;i++)k+=".";

        vector<string> board(n ,k);

        int col_check(0),diag_check(0),rdiag_check(0);

        solve(board , 0 , col_check , diag_check , rdiag_check);

        return glo_ans;

    }

};