<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:
    vector<vector<char>>grid; 
 vector<vector<string>> result;
 bool canPlaceQueen(int row,int col,int n){
 for (int i = row-1; i>=0; i--)
 {
    if (grid[i][col]=='Q')
    {
        return false;
    }
    //column check
 }
 for (int i = row-1,j=col-1; i>=0 and j>=0; i--,j--)
 {
    if (grid[i][j]=='Q')
    {
        return false;
    }
    
 }
 for (int i = row-1,j=col+1; i>=0 and j<n; i--,j++)
 {
    if (grid[i][j]=='Q')
    {
        return false;
    }
    
 }
 return true;
 }
 void f(int row,int n){
    if(row==n){
    //we get a possible answer
    vector<string>temp;
    for (int i = 0; i < n; i++)
    {    string s = "";
        for (int j = 0; j < n; j++)
        {
            s+=grid[i][j];
        }
       temp.push_back(s);
    }
    result.push_back(temp);
    return;
}
    for (int col = 0;col < n; col++)
    {
        if (canPlaceQueen(row,col,n))
        {
           grid[row][col] = 'Q';
           f(row+1,n);
           grid[row][col]='.';
        }
        
    }
 }  
    int totalNQueens(int n) {
         grid.clear();
    result.clear();
    grid.resize(n,vector<char>(n,'.'));
    f(0,n);
    return result.size();
    }
};
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