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 1:
Input: root = [1,0,2], low = 1, high = 2
Output: [1,null,2]
Example 2:
Input: root = [3,0,4,null,2,null,null,1], low = 1, high = 3
Output: [3,2,null,1]
Constraints:
+ The number of nodes in the tree is in the range [1, 10＾4].
+ 0 <= Node.val <= 10＾4
+ The value of each node in the tree is unique.
+ root is guaranteed to be a valid binary search tree.
+ 0 <= low <= high <= 10＾4