## Description

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

Given an integer n, return all distinct solutions to the n-queens puzzle.

Each solution contains a distinct board configuration of the n-queens’ placement, where 'Q' and '.' both indicate a queen and an empty space respectively.

Example:

## Approach #1 Backtracking

### Complexity Analysis

• 时间复杂度：$O(n!)$。
• 空间复杂度：$O(n^2)$。

## Approach #2 Backtracking 2

### Complexity Analysis

• 时间复杂度：$O(n!)$。
• 空间复杂度：$O(n^2)$。

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