<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<int> col,set<int> s1,set<int> s2,vector<string> temp,int i,vector<vector<string>>& ans){
        if(i==n) ans.push_back(temp);
        string s="";
        for(int j=0;j<n;j++) s+='.';
        for(int j=0;j<n;j++){
            if(col[j] || s1.find(i-j)!=s1.end() || s2.find(i+j)!=s2.end()) continue;
            else{
                col[j]=1;
                s1.insert(i-j);
                s2.insert(i+j);
                s[j]='Q';
                temp.push_back(s);
                s[j]='.';
                solve(n,col,s1,s2,temp,i+1,ans);
                col[j]=0;
                s1.erase(i-j);
                s2.erase(i+j);
                temp.pop_back();
            }
        }
    }
    vector<vector<string>> solveNQueens(int n) {
        vector<vector<string>> ans;
        vector<string> temp;
        vector<int> col(n,0);
        set<int> s1,s2;
        solve(n,col,s1,s2,temp,0,ans);
        return ans;
    }
};
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