Convert BST to Greater Tree
Convert BST to Greater Tree
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.


Input: The root of a Binary Search Tree like this:
/   \
2     13

Output: The root of a Greater Tree like this:
/   \

20     13

Approach 1:  Using Reversed inorder traversal.

Best Approach: