<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>> res;
    void solve(int col,vector<int> leftRow,vector<int> lowerDiag,vector<int> upperDiag,vector<string> queen,int n)
    {
        if(col==n)
        {
            res.push_back(queen);
            return;
        }

        for(int i=0;i<n;i++)
        {
            if(leftRow[i]==0 && lowerDiag[i+col]==0 && upperDiag[n-1+col-i]==0){
                queen[i][col]='Q';
                leftRow[i]=1;
                lowerDiag[i+col]=1;
                upperDiag[n-1+col-i]=1;
                solve(col+1,leftRow,lowerDiag,upperDiag,queen,n);
                queen[i][col]='.';
                leftRow[i]=0;
                lowerDiag[i+col]=0;
                upperDiag[n-1+col-i]=0;
            }
        }
    }
    vector<vector<string>> solveNQueens(int n) {
        vector<string> queen(n);
        string s(n,'.');
        for(int i=0;i<n;i++)
        {
            queen[i]=s;
        }
        vector<int> leftRow(n,0),lowerDiag(2*n-1,0),upperDiag(2*n-1,0);
        solve(0,leftRow,lowerDiag,upperDiag,queen,n);
        
        return res;
    }
};
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