897. Increasing Order Search Tree

题目来源：

https://leetcode.com/problems/increasing-order-search-tree/

自我感觉难度/真实难度：medium/easy

题意：

分析：

自己的代码：

优秀代码：

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def increasingBST(self, root):
        """
        :type root: TreeNode
        :rtype: TreeNode
        """
        array=self.inOrder(root)
        if not array:
            return
        newRoot=TreeNode(array[0])
        curr=newRoot
        for i in range(1,len(array)):
            curr.right=TreeNode(array[i])
            curr=curr.right
        return newRoot

    def inOrder(self,root):

        if not root:
            return []
        res=[]
        res.extend(self.inOrder(root.left))
        res.append(root.val)
        res.extend(self.inOrder(root.right))
        return res

代码效率/结果：

　　　　　　　　Runtime: 200 ms, faster than 45.33% of Python3 online submissions forIncreasing Order Search Tree.

class Solution:
  def increasingBST(self, root):
    dummy = TreeNode(0)
    self.prev = dummy
    def inorder(root):
      if not root: return None
      inorder(root.left)
      root.left = None
      self.prev.right = root
      self.prev = root
      inorder(root.right)
    inorder(root)
    return dummy.right

　　　　　　Runtime: 160 ms, faster than 63.16% of Python3 online submissions forIncreasing Order Search Tree.

自己优化后的代码：

反思改进策略：

1.前序遍历不熟悉，需要熟练编写这个代码

　　　 2.看不懂优化的第二个解答： .prev     TreeNode(0)