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Unique Binary Search Trees II
Difficulty: Medium
Category: DSA
Topics: Dynamic Programming, Backtracking, Tree, Binary Search Tree, Binary Tree
Asked at: Amazon, Google
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**.
**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]]
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**Example 2:**
**Input:** n = 1
**Output:** [[1]]
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**Constraints:**
- `1 <= n <= 8`
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