<h2><a href="https://leetcode.com/problems/n-queens/">51. N-Queens</a></h2><h3>Hard</h3><hr><div><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' placement, where <code>'Q'</code> and <code>'.'</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> [[".Q..","...Q","Q...","..Q."],["..Q.","Q...","...Q",".Q.."]]

<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> [["Q"]]

</pre>

<p>&nbsp;</p>

<p><strong>Constraints:</strong></p>

<ul>

<li><code>1 &lt;= n &lt;= 9</code></li>

</ul>

</div>