<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(int ind,int n,vector<string>&temp,vector<vector<string>>&ans){
        if(ind==n){
            ans.push_back(temp);
            return;
        }

        for(int i=0;i<n;i++){
            //decide to put at ans[i][ind]
            //check row
            int flag=0;
            for(int k=0;k<n;k++){
                if(temp[i][k]=='Q'){
                    flag++;
                    break;
                }
            }

            for(int k=1;k<n;k++){
                int l=-1*k;
                int delc[]={k,l,k,l};
                int delr[]={k,l,l,k};

                for(int m=0;m<4;m++){
                    int newr=i+delr[m];
                    int newc=ind+delc[m];

                    if(newr>=0 && newr<n && newc>=0 && newc<n){
                        if(temp[newr][newc]=='Q'){
                            flag++;
                            break;
                        }
                    }
                }
            }

            if(flag==0){
                temp[i][ind]='Q';
                solve(ind+1,n,temp,ans);
                temp[i][ind]='.';
            }

        }
    }
    int totalNQueens(int n) {
        vector<vector<string>>ans;
        string str="";
        for(int i=0;i<n;i++)
        str+='.';
        vector<string>temp(n,str);


        solve(0,n,temp,ans);
        return ans.size();
    }
};
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