<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<char>> update_vis(vector<vector<char>> vis, int row, int col ,int n)
    {
        
        vector<vector<char>>new_vis=vis;
        for(int i=0;i<n;i++)
        {  
             if(i!=col)
               new_vis[row][i]='.';
             if(i!=row)
              new_vis[i][col]='.';
            
        }

        int max_l=n;
        int k=1;
        while(k < max_l)
        {
            if(row + k < max_l && col+k <max_l)
            {
              new_vis[row+k][col+k]='.';
            }
            if(row - k >=0 && col+k <max_l)
            {
               new_vis[row-k][col+k]='.';
            }
          
            k++;
        }

        // for(int i=0;i<n;i++)
        // {
        //     for(int j=0;j<n;j++)
        //     {
        //         cout<<new_vis[i][j]<<" ";
        //     }
        //     cout<<endl;
        // }
        // cout<<endl;
        
        return new_vis;
    }
    void helper( vector<vector<string>> &ans,vector<vector<char>> vis, int col,int n){

        if(col==n)
        {
            vector<string>temp;
            for(int i=0;i<n;i++)
            { 
                string str="";
                for(int j=0;j<n;j++)
                {
                  str+=vis[i][j];
                }
                temp.push_back(str);
            }
            ans.push_back(temp);
            return ;
        }
        

        for(int row=0;row<n;row++){

            if(vis[row][col]=='0')
            {  
                
                vis[row][col]='Q';
                vector<vector<char>> new_vis=update_vis(vis,row,col,n);

                helper(ans,new_vis,col+1,n);
                vis[row][col]='0';

            }

        }
        
    }
    vector<vector<string>> solveNQueens(int n) {
        
        vector<vector<char>> vis(n,vector<char>(n,'0'));
        int col=0;
        vector<vector<string>> ans;
        helper(ans,vis,col,n);
        return ans;
    }
};
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