95.Unique Binary Search Trees II
===

###### tags: `Medium`,`DP`,`Tree`,`Backtracking`

[95. Unique Binary Search Trees II](https://leetcode.com/problems/unique-binary-search-trees-ii/)

### 題目描述

Given an integer `n`, return *all the structurally unique **BST**'s (binary search trees), which has exactly* `n` *nodes of unique values from* `1` *to* `n`. Return the answer in **any order**.

### 範例

**Example 1:**


Input: n = 3
Output: [[1,null,2,null,3],[1,null,3,2],[2,1,3],[3,1,null,null,2],[3,2,null,1]]

**Example 2:**

Input: n = 1
Output: [[1]]

**Constraints**:

* 1 <= `n` <= 8

### 解答

### Reference

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