'''
Description: 
Autor: Au3C2
Date: 2021-01-21 19:21:18
LastEditors: Au3C2
LastEditTime: 2021-01-21 19:21:47
'''
# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def convertBiNode(self, root):
        self.pre = self.ans = TreeNode(-1)
        def dfs(root):
            if not root: return
            dfs(root.left)
            root.left = None
            self.pre.right = root
            self.pre = root
            dfs(root.right)
        dfs(root)
        return self.ans.right
# 树，简单，中序遍历记录节点即可
# https://leetcode-cn.com/problems/binode-lcci/