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LeetCode

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Problem

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:

img

Input: root = [1,0,2], low = 1, high = 2
Output: [1,null,2]

Example 2:

img

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.
  • $0 <= low <= high <= 10^4$

Code

450

class Solution {
    public TreeNode trimBST(TreeNode root, int low, int high) {
        if (root == null) return root;

        if (low <= root.val && root.val <= high) {
            root.left = trimBST(root.left, low, high);
            root.right = trimBST(root.right, low, high);
        } else {
            if (root.val > high) {
                root = trimBST(root.left, low, high);
            } else if (root.val < low) {
                root = trimBST(root.right, low, high);
            }
        }

        return root;
    }
}