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
[0, 104]
. -
-104 <= Node.val <= 104
- All the values in the tree are unique.
-
root
is guaranteed to be a valid binary search tree.
Note: This question is the same as 1038: https://leetcode.com/problems/binary-search-tree-to-greater-sum-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 convertBST(self, root: Optional[TreeNode]) -> Optional[TreeNode]:
self.curr = 0
self.revinorder(root)
return root
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