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 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. Note: This question is the same as 1038: https://leetcode.com/problems/binary-search-tree-to-greater-sum-tree/ 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] Example 3: Input: root = [1,0,2] Output: [3,3,2] Example 4: Input: root = [3,2,4,1] Output: [7,9,4,10] Constraints: The number of nodes in the tree is in the range [0, 104]. -104 <= Node.val <= 104 All the values in the tree are unique. root is guaranteed to be a valid binary search tree.