<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 count = 0;
    void mark(int i,int j,vector<vector<int>> &vis){
        for(int k=0;k<vis.size();k++){
            vis[k][j] = 1;
        }
        for(int k=0;k<vis[0].size();k++){
            vis[i][k] = 1;
        }
        int row = i;
        int col = j;
        while(row >= 0 && col>= 0){
            vis[row][col] = 1;
            row--;
            col--;
        }
        row = i;
        col = j;
        while(row<vis.size() && col<vis[0].size()){
            vis[row][col] = 1;
            row++;
            col++;
        }
        row = i;
        col = j;
        while(row >= 0 && col <vis[0].size()){
            vis[row][col] = 1;
            row--;
            col++;
        }
        row = i;
        col = j;
        while(col >= 0 && row <vis.size()){
            vis[row][col] = 1;
            col--;
            row++;
        }
    }


    void check(int i,int n,vector<vector<int>> vis,vector<string> curr){
        if(n == 0){
            count++;
            return;
        }
        if(i == vis.size()){
            return;
        }
        vector<vector<int>> help = vis;
        for(int j=0;j<vis[0].size();j++){
            if(vis[i][j] == 0){
                string temp = curr[i];
                temp[j] ='Q';
                curr[i] = temp;
                mark(i,j,vis);
                check(i+1,n-1,vis,curr);
                vis = help;
                temp[j] = '.';
                curr[i] = temp;
            }
        }

    }

    void solveNQueens(int n) {
        vector<vector<int>> vis(n,vector<int>(n,0));
        vector<string> curr(n);
        string temp = "";
        for(int i=0;i<n;i++){
            temp = temp + ".";
        }
        for(int i=0;i<n;i++){
            curr[i] = temp;
        }
        check(0,n,vis,curr);
    }

    int totalNQueens(int n) {
        solveNQueens(n);
        return count;
    }
};
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