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# [95. Unique Binary Search Trees II](https://leetcode.com/problems/unique-binary-search-trees-ii/)
## 题目
Given an integer *n*, generate all structurally unique **BST's** (binary search trees) that store values 1 ... *n*.
**Example:**
Input: 3
Output:
[
[1,null,3,2],
[3,2,null,1],
[3,1,null,null,2],
[2,1,3],
[1,null,2,null,3]
]
Explanation:
The above output corresponds to the 5 unique BST's shown below:
1 3 3 2 1
\ / / / \ \
3 2 1 1 3 2
/ / \ \
2 1 2 3
## 题目大意
给定一个整数 n生成所有由 1 ... n 为节点所组成的二叉搜索树。
## 解题思路
- 输出 1~n 元素组成的 BST 所有解。这一题递归求解即可。外层循环遍历 1~n 所有结点,作为根结点,内层双层递归分别求出左子树和右子树。