Given 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 sum of all keys greater than the original key in BST.
Example:
Input: The root of a Binary Search Tree like this: 5 / 2 13 Output: The root of a Greater Tree like this: 18 / 20 13
/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */ public class Solution { int sum = 0; public TreeNode convertBST(TreeNode root) { if (root == null) return null; convert(root); return root; } public void convert(TreeNode root) { if (root == null) return ; convert(root.right); root.val += sum; sum = root.val; convert(root.left); } }