538. Convert BST to Greater Tree 二叉搜索树转换为更大树
Given 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.
Example:
Input: The root of a Binary Search Tree like this: 5 / \ 2 13 Output: The root of a Greater Tree like this: 18 / \ 20 13
题意:给出二叉搜索树,每一个节点累加比自己更大的值
解法:根据二叉搜索树的特性可知,按照 右->根->左的顺序遍历节点
# Definition for a binary tree node.
# class TreeNode(object):
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution(object):
def convertBST(self, root):
"""
:type root: TreeNode
:rtype: TreeNode
"""
self.helper(root)
return root
sum = 0
def helper(self, node):
if(node):
self.helper(node.right)
node.val += self.sum
self.sum = node.val
self.helper(node.left)