LeetCode in Kotlin

669. Trim a Binary Search Tree

Medium

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

import com_github_leetcode.TreeNode

/*
 * Example:
 * var ti = TreeNode(5)
 * var v = ti.`val`
 * Definition for a binary tree node.
 * class TreeNode(var `val`: Int) {
 *     var left: TreeNode? = null
 *     var right: TreeNode? = null
 * }
 */
class Solution {
    fun trimBST(root: TreeNode?, l: Int, r: Int): TreeNode? {
        if (root == null) {
            return root
        }
        if (root.`val` > r) {
            return trimBST(root.left, l, r)
        }
        if (root.`val` < l) {
            return trimBST(root.right, l, r)
        }
        root.left = trimBST(root.left, l, r)
        root.right = trimBST(root.right, l, r)
        return root
    }
}

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