<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:
bool safe(vector<vector<char>>&board,int i,int j,int n){
    if(i==0)return true;
    vector<pair<int,int>>vec;
    for(int k=0;k<i;k++){
        for(int l=0;l<n;l++){
            if(board[k][l]=='Q')
            vec.push_back({k,l});
        }
    }
    for(auto x:vec){
        int a=x.first;
        int b=x.second;
        if(j==b||a+b==i+j||a-b==i-j)return false;
    }
    return true;
}
 int solve( vector<vector<char>>&board,int i,
   int n){
        if(i==n){
          
            return 1;
        }
        int ans=0;
        for(int j=0;j<n;j++){
            if(safe(board,i,j,n)){
                board[i][j]='Q';
               ans+= solve(board,i+1,n);
                board[i][j]='.';
            }
        }
        return ans;

    }
    int totalNQueens(int n) {
          vector<vector<char>>board(n,vector<char>(n,'.'));
       
       return solve(board,0,n);
       
    }
};
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