<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>the number of distinct solutions to the&nbsp;<strong>n-queens puzzle</strong></em>.</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> 2
<strong>Explanation:</strong> There are two distinct solutions to the 4-queens puzzle as shown.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> n = 1
<strong>Output:</strong> 1
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= n &lt;= 9</code></li>
</ul>

class Solution {
public:
void nqueens(int i,int n,vector<vector<bool>>visited,vector<string>s,vector<vector<string>>&ans){
        if(i==n){
            ans.push_back(s);
            return;
        }
        for(int j=0;j<n;j++){
            if(visited[i][j]==0){
                vector<vector<bool>>v(n,vector<bool>(n,0));
                v=visited;
                for(int r=0;r<n;r++){
                   v[r][j]=1;
                }
                for(int c=0;c<n;c++){
                   v[i][c]=1;
                }
                int r=i,c=j;
                while(r>=0&&c>=0){
                    v[r][c]=1;
                    r--,c--;
                }
                r=i,c=j;
                while(r>=0&&c<n){
                    v[r][c]=1;
                    r--,c++;
                }
                r=i,c=j;
                while(r<n&&c<n){
                    v[r][c]=1;
                    r++,c++;
                }
                r=i,c=j;
                while(r<n&&c>=0){
                    v[r][c]=1;
                    r++,c--;
                }
                string row="";
                for(int k=0;k<n;k++){
                    if(k==j){
                        row+="Q";
                        continue;
                    }
                    row+=".";
                }
                s.push_back(row);
                nqueens(i+1,n,v,s,ans);
                s.pop_back();
            }
        }
    }
    int totalNQueens(int n) {
         vector<vector<string>>ans;
        vector<string>s;
        vector<vector<bool>>visited(n,vector<bool>(n,0));
        nqueens(0,n,visited,s,ans);
        return ans.size();
    }
};
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