<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(vector<vector<string>>&ans,vector<string>t,int n,int row,int col,unordered_map<int,bool>m,unordered_map<int,bool>m1,unordered_map<int,bool>m2){
        if(row>=n){
            ans.push_back(t);
            return;
        }
        for(int col = 0;col<n;col++){
             if(!m[col] && !m1[row+col] && !m2[n-1 + col-row]){
                t[row][col]='Q';
                m[col]=true;
                m1[row+col] = true;
                m2[n-1 + col-row] = true;
                solve(ans,t,n,row+1,0,m,m1,m2);
                m[col]=false;
                m1[row+col] = false;
                m2[n-1 + col-row] = false;
                t[row][col]='.';
             }
        }
    }

    vector<vector<string>> solveNQueens(int n) {
        vector<vector<string>> ans;
        vector<string>t;
        string str="";
        for(int i=0;i<n;i++) str+='.';
        for(int i=0;i<n;i++) t.push_back(str);
        unordered_map<int,bool>m;
        unordered_map<int,bool>m1;
        unordered_map<int,bool>m2;
        solve(ans,t,n,0,0,m,m1,m2);
        return ans;
    }
};
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