<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:
    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;
        }
        int c=column;
        for(int i=row;i<n;i++){
            if(c<n) {
                board[i][c]=0;
            }
            else break;
            c++;
        }
        c=column;
        for(int i=row;i>=0;i--){
            if(c<n) {
                board[i][c]=0;
            }
            else break;
            c++;
        }
    }
    vector<vector<string>> calculateAns(int n, int column, vector<vector<int>> board, vector<string> str) {
        vector<vector<string>> ans;
        if (column >= n) {
            ans.push_back(str);
            return ans;
        }
        for (int i = 0; i < board.size(); i++) {
            if (board[i][column]) {
                vector<vector<int>> newBoard = board;
                markBoard(newBoard, i, column);
                string s(n, '.');
                s[i] = 'Q';
                str.push_back(s);
                vector<vector<string>> subAns = calculateAns(n, column + 1, newBoard, str);
                ans.insert(ans.end(), subAns.begin(), subAns.end());
                str.pop_back();
            }
        }
        return ans;
    }

    vector<vector<string>> solveNQueens(int n) {
        vector<vector<int>> board(n, vector<int>(n, 1));
        vector<string> str;
        return calculateAns(n,0,board,str);
    }
};
41753