<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>> v;
    void solve(vector<string> a, int n,set<int> s, int r, int e, set<pair<int,int>> p){
        if(s.size()==n){
            v.push_back(a);
            return;
        }
        if(r>n){
            return;
        }
        int f=0;
        for(int i = 0 ; i <n ; i++){
            // if(s.find(i)!=s.end() || s.find(i-1)!=s.end() || s.find(i+1)!=s.end()){
            //     continue;
            // }
            int f=0;
            for(int j = 1 ; j<=r ; j++){
                if(p.find({i-j,r-j})!=p.end()){
                    f=1;
                    break;
                }
            }
            for(int j = 1 ; j<=r ; j++){
                if(p.find({i+j,r-j})!=p.end()){
                    f=1;
                    break;
                }
            }
            if(((i==e || i==e-1 || i==e+1) && e!=-1) || s.find(i)!=s.end() || f==1){
                continue;
            }
            else{
                f=1;
                s.insert(i);
                string q = "";
                for(int j = 0 ; j< n ; j++){
                    if(j==i){
                        q+="Q";
                    }
                    else{
                        q+=".";
                    }
                }
                p.insert({i,r});
                a.push_back(q);
                solve(a,n,s,r+1,i,p);
                p.erase({i,r});
                a.pop_back();
                s.erase(i);
            }
        }
        if(f==0){
            return;
        }
    }
    vector<vector<string>> solveNQueens(int n) {
        vector<string> a;
        set<int> s;
        set<pair<int,int>> p;
        solve(a,n,s,0,-1,p);
        return v;
    }
};
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