'''
Description: 
Autor: Au3C2
Date: 2021-03-15 16:36:26
LastEditors: Au3C2
LastEditTime: 2021-03-15 16:36:57
'''
# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def increasingBST(self, root: TreeNode) -> TreeNode:
        def recursion(root):
            
            if not root:
                return
            
            recursion(root.left)

            # self.thisNode = TreeNode(root.val)
            root.left = None
            if not self.lastNode:
                self.lastNode = root
                self.head = root
            else:
                self.lastNode.right = root
                self.lastNode = root
            
            recursion(root.right)

        self.lastNode = None     
        self.head = None

        recursion(root)
        return self.head

# 树，dfs，简单
# https://leetcode-cn.com/problems/increasing-order-search-tree/