【leetcode】538. Convert BST to Greater Tree

题目如下：

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     13Output: The root of a Greater Tree like this:18/   \20     13

解题思路：一时卡壳了，只想出了一个很挫的方法，把所有节点的值都取出来，然后找出每个节点的所有比其大的值的和，这个值就是这个节点的值要加上的大小，最后再遍历一次树修改节点。

代码如下：

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = Noneclass Solution(object):l = []dic = {}def traverse(self,node,mode):if node == None:returnif mode == 1:self.l.append(node.val)else:node.val += self.dic[node.val]if node.left != None:self.traverse(node.left,mode)if node.right != None:self.traverse(node.right,mode)def convertBST(self, root):""":type root: TreeNode:rtype: TreeNode"""self.l = []self.dic = {}self.traverse(root,1)ul = sorted(list(set(self.l)))total = 0for i in ul[::-1]:self.dic[i] = totaltotal += iself.traverse(root, 0)return root

转载于:https://www.cnblogs.com/seyjs/p/10208410.html

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