<p>The <strong>n-queens</strong> puzzle is the problem of placing <code>n</code> queens on an <code>n x n</code> chessboard such that no two queens attack each other.</p>

<p>Given an integer <code>n</code>, return <em>all distinct solutions to the <strong>n-queens puzzle</strong></em>. You may return the answer in <strong>any order</strong>.</p>

<p>Each solution contains a distinct board configuration of the n-queens&#39; placement, where <code>&#39;Q&#39;</code> and <code>&#39;.&#39;</code> both indicate a queen and an empty space, respectively.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2020/11/13/queens.jpg" style="width: 600px; height: 268px;" />
<pre>
<strong>Input:</strong> n = 4
<strong>Output:</strong> [[&quot;.Q..&quot;,&quot;...Q&quot;,&quot;Q...&quot;,&quot;..Q.&quot;],[&quot;..Q.&quot;,&quot;Q...&quot;,&quot;...Q&quot;,&quot;.Q..&quot;]]
<strong>Explanation:</strong> There exist two distinct solutions to the 4-queens puzzle as shown above
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> n = 1
<strong>Output:</strong> [[&quot;Q&quot;]]
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= n &lt;= 9</code></li>
</ul>

class Solution {
public:
    vector<vector<string>> final_result;
    int N;
    unordered_set<int> cols;
    unordered_set<int> diag;//right
    unordered_set<int> antidiag;//left 
void NQueen_fn(vector<string> &board ,int row ){//yha hum row pr daalenge queen ko and check krenge ki vo place kr skti h ya nhi
   if(row>=N) final_result.push_back(board);

   for( int col=0; col<N;col++){
    int diagconst = row+col;
    int antidiagconst = row-col;
       if(cols.find(col) != cols.end() || diag.find(diagconst)!= diag.end() || antidiag.find(antidiagconst)!=antidiag.end()) {
            continue;
          
        }
            cols.insert(col);
            diag.insert(diagconst);
            antidiag.insert(antidiagconst);
            board[row][col] ='Q';
            NQueen_fn(board, row+1);
            cols.erase(col);
            diag.erase(diagconst);
            antidiag.erase(antidiagconst);
            board[row][col] ='.';
   }
   

}

    vector<vector<string>> solveNQueens(int n) {
         N=n;
        vector<string> board(n, string(n,'.'));
        NQueen_fn(board,0); // Call the NQueen function to solve the N-Queen problem
        return final_result;
        
    }
};
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