<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 helper(int n, vector<string> &curr, vector<vector<string>> &ans, int row, set<int> col, set<int> diag, set<int> adiag){
        cout<<n<<endl;
        for(int i=0;i<curr.size();i++){
            for(int j=0;j<curr.size();j++){
                cout<<curr[i][j]<<" ";
            }
            cout<<endl;
        }
        if(n==0){
            ans.push_back(curr);
            return;
        }


        for(int i=0;i<curr.size();i++){
            if(col.find(i)==col.end() && diag.find(row-i) == diag.end() && adiag.find(row+i) == adiag.end()){
                curr[row][i]='Q';
                col.insert(i);
                diag.insert(row-i);
                adiag.insert(row+i);
                helper(n-1, curr, ans, row+1, col, diag, adiag);
                curr[row][i]='.';
                col.erase(i);
                diag.erase(row-i);
                adiag.erase(row+i);
            }
        }
        return;

    }
    vector<vector<string>> solveNQueens(int n) {
        vector<string> curr;
        string temp="";
        int c=n;
        while(c--){
            temp+='.';
        }
        c=n;
        while(c--){
            curr.push_back(temp);
        }
        vector<vector<string>> ans;
        set<int> col, diag, adiag;
        helper(n, curr, ans, 0,  col, diag, adiag);
        return ans;
    }
};
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