<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 solve(int n,vector<string> temp,vector<vector<string>> &ans,int col,vector<int> upperdiagonal,vector<int> lowerdiagonal,vector<int> leftrow){
    if(col==n){
        ans.push_back(temp);
        return;
    }
    for(int row=0;row<n;row++){
        if(leftrow[row]==0 && upperdiagonal[n-1+col-row]==0 && lowerdiagonal[row+col]==0)
        {
            temp[row][col]='Q';
            leftrow[row]=1;
            lowerdiagonal[row+col]=1;
            upperdiagonal[n-1+col-row]=1;
            solve(n,temp,ans,col+1,upperdiagonal,lowerdiagonal,leftrow);
            temp[row][col]='.';
            leftrow[row]=0;
            lowerdiagonal[row+col]=0;
            upperdiagonal[n-1+col-row]=0;   
        }
    }
}
    vector<vector<string>> solveNQueens(int n) {
        vector<vector<string>> ans;
        vector<string> temp(n);
        string s(n,'.');
        vector<int> upperdiagonal(2*n-1,0),lowerdiagonal(2*n-1,0),leftrow(n,0);
        for(int i=0;i<n;i++)
        temp[i]=s;
        int col=0;
        solve(n,temp,ans,col,upperdiagonal,lowerdiagonal,leftrow);
        return ans;
    }
};
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