<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>all distinct solutions to the <strong>n-queens puzzle</strong></em>. You may return the answer in <strong>any order</strong>.</p>

<p>Each solution contains a distinct board configuration of the n-queens&#39; placement, where <code>&#39;Q&#39;</code> and <code>&#39;.&#39;</code> both indicate a queen and an empty space, respectively.</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> [[&quot;.Q..&quot;,&quot;...Q&quot;,&quot;Q...&quot;,&quot;..Q.&quot;],[&quot;..Q.&quot;,&quot;Q...&quot;,&quot;...Q&quot;,&quot;.Q..&quot;]]
<strong>Explanation:</strong> There exist two distinct solutions to the 4-queens puzzle as shown above
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> n = 1
<strong>Output:</strong> [[&quot;Q&quot;]]
</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<string>> ans;
    void markBoard(vector<vector<int>>& board,int row,int column){
        int n= board.size();
        for(int i=column;i<n;i++){
            board[row][i]=0;
            // cout<<"i="<<row<<" c="<<i<<endl;
        }
        int c=column;
        for(int i=row;i<n;i++){
                // cout<<"rdi="<<i<<" c="<<c<<endl;
            if(c<n) {
                board[i][c]=0;
            }
            else break;
            c++;
        }
        c=column;
        for(int i=row;i>=0;i--){
            
                // cout<<"rui="<<i<<" c="<<c<<endl;
            if(c<n) {
                board[i][c]=0;
            }
            else break;
            c++;
        }
    }
    void calculateAns(int n,int column,vector<vector<int>> board,vector<string> str){
       if(column>=n){
        ans.push_back(str);
        return;
       }
       for(int i=0;i<board.size();i++){
        if(board[i][column]){
            vector<vector<int>> newBoard=board;
            markBoard(newBoard,i,column);
            // cout<<"Board for cell="<<i<<" "<<column<<endl;
            // for(int k=0;k<board.size();k++){
            //     for(int m=0;m<board.size();m++){
            //         cout<<newBoard[k][m]<<" ";
            //     } cout<<endl;
            // }
            string s(n,'.');
            s[i]='Q';
            str.push_back(s);
            calculateAns(n,column+1,newBoard,str);
            str.pop_back();
        }
       }
    }

    vector<vector<string>> solveNQueens(int n) {
        vector<vector<int>> board(n, vector<int>(n, 1));
        vector<string> str;
        calculateAns(n,0,board,str);
        return ans;
    }
};
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