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 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:
Note: This question is the same as 538: https://leetcode.com/problems/convert-bst-to-greater-tree/
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]
Input: root = [0,null,1] Output: [1,null,1]
Input: root = [1,0,2] Output: [3,3,2]
Input: root = [3,2,4,1] Output: [7,9,4,10]
0 <= Node.val <= 100
rootis guaranteed to be a valid binary search tree.