<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 {
private:
    bool isPoss(vector<string>&t , int row , int col,int n){
        int c = col ;
        int cl = col -1 ;
        int cr = col + 1 ;

        while(row >= 0){
            if(c >= 0 and c < n and t[row][c] == 'Q'){
                return false ;
            }
            else if(cl >= 0 and cl < n and t[row][cl] == 'Q'){
                return false ;
            }
            else if(cr >= 0 and cr < n and t[row][cr] == 'Q'){
                return false ;
            }
            cl -= 1 ;
            cr += 1 ;
            row -= 1 ;
        }

        return true ;
    }
    void func(int row , int n , vector<string>&temp , vector<vector<string>> &ans){
        if(row == n){
            ans.push_back(temp) ;
            return ;
        }

        for(int i = 0 ; i < n ; i++){
            if(isPoss(temp,row-1,i,n)){
                temp[row][i] = 'Q' ;
                func(row+1,n,temp,ans) ;
                temp[row][i] = '.' ; // backtrack :: 
            }
        }

        return ;
    }
public:
    vector<vector<string>> solveNQueens(int n) {
        vector<vector<string>> ans  ;
        string t = "" ;
        for(int i = 0 ; i < n ; i++){
            t += '.' ;
        } 
        vector<string> temp(n,t) ;
        func(0,n,temp,ans) ;
        
        return ans ;

    }
};
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