LeetCode-in-Java
1038. Binary Search Tree to Greater Sum Tree
Medium
Given the root of a Binary Search Tree (BST), convert it to a Greater Tree such that every key of the original BST is changed to the original key plus the sum of all keys greater than the original key in BST.
As a reminder, a binary search tree is a tree that satisfies these constraints:
- The left subtree of a node contains only nodes with keys less than the node’s key.
- The right subtree of a node contains only nodes with keys greater than the node’s key.
- Both the left and right subtrees must also be binary search trees.
Example 1:
Input: root = [4,1,6,0,2,5,7,null,null,null,3,null,null,null,8]
Output: [30,36,21,36,35,26,15,null,null,null,33,null,null,null,8]
Example 2:
Input: root = [0,null,1]
Output: [1,null,1]
Constraints:
- The number of nodes in the tree is in the range
[1, 100]. 0 <= Node.val <= 100- All the values in the tree are unique.
Note: This question is the same as 538: https://leetcode.com/problems/convert-bst-to-greater-tree/
Solution
import com_github_leetcode.TreeNode;
/*
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
public class Solution {
private int greaterSum = 0;
public TreeNode bstToGst(TreeNode root) {
if (root.right != null) {
bstToGst(root.right);
}
greaterSum = root.val = greaterSum + root.val;
if (root.left != null) {
bstToGst(root.left);
}
return root;
}
}