LeetCode538:Convert BST to Greater Tree
阿新 • • 發佈:2019-01-05
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
LeetCode:連結
二叉查詢樹(英語:Binary Search Tree),也稱為二叉搜尋樹、有序二叉樹(ordered binary tree)或排序二叉樹(sorted binary tree),是指一棵空樹或者具有下列性質的二叉樹:
- 若任意節點的左子樹不空,則左子樹上所有節點的值均小於它的根節點的值;
- 若任意節點的右子樹不空,則右子樹上所有節點的值均大於它的根節點的值;
- 任意節點的左、右子樹也分別為二叉查詢樹;
- 沒有鍵值相等的節點。
二叉搜尋樹的中序遍歷結果是元素值由小到大有序的嗎?這題要求把每個結點的值更新為比其大的結點值之和,那倒著來一遍中序遍歷就好了。也就是說,由大到小遍歷結點,每次累加比當前結點值大的和,賦值給當前結點就好了。“右 - 根 - 左”順序遍歷BST。
# 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.total = 0 def traverse(root): if not root: return None traverse(root.right) root.val += self.total self.total = root.val traverse(root.left) traverse(root) return root