## DEV Community

Abhishek Chaudhary

Posted on

# Trim a Binary Search Tree

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, 104]`.
• `0 <= Node.val <= 104`
• The value of each node in the tree is unique.
• `root` is guaranteed to be a valid binary search tree.
• `0 <= low <= high <= 104`

SOLUTION:

``````# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
def trimBST(self, root: Optional[TreeNode], low: int, high: int) -> Optional[TreeNode]:
if root:
if low <= root.val <= high:
root.left = self.trimBST(root.left, low, high)
root.right = self.trimBST(root.right, low, high)
elif root.val < low:
root = self.trimBST(root.right, low, high)
else:
root = self.trimBST(root.left, low, high)
return root
``````