README_CN.md

538. 把二叉搜索树转换为累加树

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

题解 (Python)

1. 中序遍历

# 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:
        nodes = []
        curr = root
        sum = 0

        while nodes or curr:
            while curr:
                nodes.append(curr)
                curr = curr.right

            curr = nodes.pop()

            sum += curr.val
            curr.val = sum

            curr = curr.left

        return root