<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:
   void func(int j , int n , vector<int> row , vector<int> left ,
      vector<int> right ,   vector<string> mat , vector<vector<string>> &res )
        {
            if(j == n)
              {
                res.push_back(mat) ;
                return ;
              }

            for(int i = 0 ; i < n ; i++)
              {
                  if( (row[i] == 0) &&  (right[i+j] == 0) && (left[n-1 - i + j] == 0) )
                    {
                        mat[i][j] = 'Q' ;
                        row[i] = 1 ;
                        right[i+j] = 1 ;
                        left[n-1 - i + j] = 1 ;

                        func( j + 1 , n , row ,  left , right ,  mat , res) ;

                        mat[i][j] = '.' ;
                        row[i] = 0 ;
                        right[i+j] = 0 ;
                        left[n-1 - i + j] = 0 ;
                    }
              }

        }

    vector<vector<string>> solveNQueens(int n)
     {
        string s = "" ;

        for(int i = 0 ; i < n ; i++)
          s.push_back('.') ;
  
        vector<string>  mat(n , s) ;
        vector<vector<string>> res ;

        vector<int> row(n , 0) ;

        vector<int> left(2*n - 1 , 0) ;
        vector<int> right(2*n - 1 , 0);

        func(0 , n , row , left , right , mat , res) ;

        return res ;
     }

};
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