给定一个二叉搜索树（Binary Search Tree），把它转换成为累加树（Greater Tree)，使得每个节点的值是原来的节点值加上所有大于它的节点值之和。
例如：
输入: 二叉搜索树: 5 / \ 2 13
输出: 转换为累加树: 18 / \ 20 13
Js
/**
* Definition for a binary tree node.
* function TreeNode(val) {
* this.val = val;
* this.left = this.right = null;
* }
*/
/**
* @param {TreeNode} root
* @return {TreeNode}
*/
var convertBST = function(root) {
num = 0
function dfs(root){
if (!root) {
return null
}
dfs(root.right)
num += root.val
root.val = num
dfs(root.left)
return root
}
return dfs(root)
}
Py
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution:
def convertBST(self, root: TreeNode) -> TreeNode:
self.a = 0
def dfs(root):
if not root:
return None
dfs(root.right)
self.a+=root.val
root.val = self.a
dfs(root.left)
return root
return dfs(root)
