<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 {
    bool check(vector<vector<int>> &qpos, int col, int row){
        for(auto queens:qpos){
            if(queens[0]==row){return false;}
            if(abs(queens[0]-row)==abs(queens[1]-col)){return false;}
        }
        return true;
    }
    void helper(int &n, vector<vector<int>> &qpos, int col, int &cnt){
        if(col>n){
            cnt++;
            return;
            }
        for(int i = 1; i<=n; i++){
            if(check(qpos,col,i)){
                qpos.push_back({i,col});
                helper(n,qpos,col+1,cnt);
                qpos.pop_back();
            }
        }
        return;
    }
public:
    int totalNQueens(int n) {
        vector<vector<int>> qpos;
        int cnt = 0;
        helper(n,qpos,1, cnt);
        return cnt;
    }
};
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