<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> > finalans;
    void findqueen(unordered_map<int, int> m_vertical, unordered_map<int, int> m_minus, unordered_map<int, int> m_plus, vector<string> ans, int n, int row){

        if(row == n){
            finalans.push_back(ans);
            return;
        }

            for(int j = 0; j < n; j++){
                //over cols
            if (m_vertical.find(j) == m_vertical.end() &&
                m_minus.find(row - j) == m_minus.end() &&
                m_plus.find(row + j) == m_plus.end()) {
                // Place queen
                m_vertical[j] = 1;
                m_minus[row - j] = 1;
                m_plus[row + j] = 1;

                string temp(n, '.');
                temp[j] = 'Q';
                ans.push_back(temp);

                // Recurse to the next row
                findqueen(m_vertical, m_minus, m_plus, ans, n, row + 1);

                // Backtrack
                ans.pop_back();
                m_vertical.erase(j);
                m_minus.erase(row - j);
                m_plus.erase(row + j);

            }
        }
    }
    vector<vector<string>> solveNQueens(int n) {
        unordered_map<int, int> m_vertical;
         unordered_map<int, int> m_minus;
         unordered_map<int, int> m_plus;
          vector<string> ans;
        findqueen(m_vertical, m_minus, m_plus, ans, n, 0);
        return finalans;

    }
};
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