leetcode刷题python之恢复二叉搜索树

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

class Solution:
    def recoverTree(self, root: TreeNode) -> None:
        """
        Do not return anything, modify root in-place instead.
        """
        FirstNode = None
        SecondNode = None
        pre = TreeNode(float("-inf"))

        p = root
        stack = []
        while p or stack:
            while p:
                stack.append(p)
                p = p.left
            p = stack.pop()

            if not FirstNode and pre.val > p.val:
                FirstNode = pre
            if FirstNode and pre.val > p.val:
                SecondNode = p
            
            pre = p
            p = p.right
            
        FirstNode.val, SecondNode.val = SecondNode.val, FirstNode.val