<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 solve(vector<vector<string>>& R, vector<string> C, int i,int n, vector<pair<int,int>> M){
        if(i>=n){
            R.push_back(C);
            return;
        }
        for(int j=0;j<n;j++){
            bool go=true;
            for(int x=0;x<M.size();x++){
                if((j==M[x].second)||(abs(i-M[x].first)==abs(j-M[x].second)))
                {
                  go=false;
                }
            }
            if(go){ 
                C[i][j]='Q';
                pair<int,int> P(i,j);
                M.push_back(P);
                solve(R,C,i+1,n,M);
                M.pop_back();
                C[i][j]='.';
            }
        }
    } 
    vector<vector<string>> solveNQueens(int n) {
        vector<vector<string>> R;
        vector<string> C(n, string(n,'.'));
        vector<pair<int,int>> M;
        
        solve(R,C,0,n,M); 
        return R;
    }
    int totalNQueens(int n) {
        vector<vector<string>> R;
        vector<string> C(n, string(n,'.'));
        vector<pair<int,int>> M;
        solve(R,C,0,n,M); 
        return R.size();
    }
};
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