1038. Binary Search Tree to Greater Sum Tree

https://leetcode.com/problems/binary-search-tree-to-greater-sum-tree

Description

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 538: https://leetcode.com/problems/convert-bst-to-greater-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 [1, 100].

• 0 <= Node.val <= 100

• All the values in the tree are unique.

• root is guaranteed to be a valid binary search tree.

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