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1038. Binary Search Tree to Greater Sum Tree

Given the root of a binary search tree with distinct values, modify it so that every node has a new value equal to the sum of the values of the original tree that are greater than or equal to node.val.

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: [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]

Note:

  1. The number of nodes in the tree is between 1 and 100.
  2. Each node will have value between 0 and 100.
  3. The given tree is a binary search tree.

Solutions (Python)

1. Inorder Traversal

# Definition for a binary tree node.# class TreeNode:# def __init__(self, x):# self.val = x# self.left = None# self.right = NoneclassSolution: defbstToGst(self, root: TreeNode) ->TreeNode: stack= [] curr=rootsum=0whilestackorcurr: whilecurr: stack.append(curr) curr=curr.rightcurr=stack.pop() sum+=curr.valcurr.val=sumcurr=curr.leftreturnroot
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