52\. N-Queens II

Hard

The **n-queens** puzzle is the problem of placing `n` queens on an `n x n` chessboard such that no two queens attack each other.

Given an integer `n`, return _the number of distinct solutions to the **n-queens puzzle**_.

**Example 1:**

![](https://assets.leetcode.com/uploads/2020/11/13/queens.jpg)

**Input:** n = 4

**Output:** 2

**Explanation:** There are two distinct solutions to the 4-queens puzzle as shown. 

**Example 2:**

**Input:** n = 1

**Output:** 1 

**Constraints:**

*   `1 <= n <= 9`