# Leetcode 538 - Convert BST to greater tree

`Note:`

- Wasted too much time on a wrong solution even if I knew that I should do
`reverse inorder traversal`

. Need to pratice more binary tree questions using recursion. - We just need a global variable
`acc`

to store sums. That’s it.

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] |

1 | /** |