<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 row,int n,set<int>br,set<int>bc,set<int>bd1,set<int>bd2,vector<string>&board,set<vector<string>>&ans)
    {
        if(row == n){

            if(ans.find(board) == ans.end()){
                ans.insert(board);
            }
            return;
        }
        for(int j = 0;j < n; j++)
        {
            // for(int j=0;j<N;j++)
            // {
                if(bc.find(j) != bc.end() || bd1.find(row - j) != bd1.end() || bd2.find(row + j) != bd2.end()){
                    continue;
                }else{
                    board[row][j] = 'Q';
                    bc.insert(j);
                    bd1.insert(row - j);
                    bd2.insert(row + j);
                    solve(row + 1,n,br,bc,bd1,bd2,board,ans);
                    board[row][j] = '.';
                    br.erase(row);
                    bc.erase(j);
                    bd1.erase(row - j);
                    bd2.erase(row + j);
                }
            // }
        }
    }
    vector<vector<string>> solveNQueens(int n) {
        set<int>br,bc,bd1,bd2;
        vector<string>board(n,string(n,'.'));
        set<vector<string>>ans;
        solve(0,n,br,bc,bd1,bd2,board,ans);

        vector<vector<string>>res(ans.begin(),ans.end());
        return res;

    }
};
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