【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 13 Output: 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 = None class Solution(object):
l = []
dic = {}
def traverse(self,node,mode):
if node == None:
return
if 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 = 0
for i in ul[::-1]:
self.dic[i] = total
total += i
self.traverse(root, 0)
return root
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