# Leetcode 669 - Trim a BST

Note:

• Look out cases in which we need to keep trimming a subtree.
• Recursion:
• Return value is a node, so base case is return null and result is return root.
• Techniques we learned: root.left = recur(...), root.right = recur(...).

Given the root of a binary search tree and the lowest and highest boundaries as low and high, trim the tree so that all its elements lies in [low, high]. Trimming the tree should not change the relative structure of the elements that will remain in the tree (i.e., any node’s descendant should remain a descendant). It can be proven that there is a unique answer.

Return the root of the trimmed binary search tree. Note that the root may change depending on the given bounds.

Example: