Leetcode•Jun 05, 2025
Trim a Binary Search Tree
Hazrat Ali
Leetcode
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]
Solution
/**
* @param {TreeNode} root
* @param {number} L
* @param {number} R
* @return {TreeNode}
*/
const trimBST = function(root, L, R) {
if (!root) {
return null;
}
const left = trimBST(root.left, L, R);
const right = trimBST(root.right, L, R);
if (root.val < L) {
return right;
}
if (root.val > R) {
return left;
}
root.left = left;
root.right = right;
return root;
};