## DEV Community

Abhishek Chaudhary

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# Binary Search Tree to Greater Sum Tree

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]
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]

Constraints:

• The number of nodes in the tree is in the range `[1, 100]`.
• `0 <= Node.val <= 100`
• All the values in the tree are unique.

Note: This question is the same as 538: https://leetcode.com/problems/convert-bst-to-greater-tree/

SOLUTION:

``````# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
def revinorder(self, root):
if root:
self.revinorder(root.right)
self.curr += root.val
root.val = self.curr
self.revinorder(root.left)

def bstToGst(self, root: TreeNode) -> TreeNode:
self.curr = 0
self.revinorder(root)
return root
``````