<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:
int ans=0;
    bool f1(int x,int y,vector<vector<int>>&v){
        for(auto it:v){
            int a=it[0],b=it[1];
            if(a==x || b==y || abs(a-x)==abs(b-y)) return false;
        }
        return true;
    }
    void f(int idx,int n,vector<vector<int>>&v){
        if(idx==n) ans++;
        int ans=0;
        for(int i=0;i<n;i++){
            int x=idx,y=i;
            if(f1(x,y,v)){
                v.push_back({x,y});
                f(idx+1,n,v);
                v.pop_back();
            }
        }
        return;
    }
    int totalNQueens(int n) {
        vector<vector<int>>v;
        f(0,n,v);
        return ans;
    }
};
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