[LeetCode]99 恢复二叉搜索树

题目描述

二叉搜索树中的两个节点被错误地交换。

请在不改变其结构的情况下，恢复这棵树。

示例1:

输入: [1,3,null,null,2]
   1
  /
 3
  \
   2
输出: [3,1,null,null,2]
   3
  /
 1
  \
   2

示例2:

输入: [3,1,4,null,null,2]
  3
 / \
1   4
   /
  2
输出: [2,1,4,null,null,3]
  2
 / \
1   4
   /
  3

代码

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# 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):
        """
        :type root: TreeNode
        :rtype: void Do not return anything, modify root in-place instead.
        """
        pre = None
        first, second = None, None
        while root:
            if root.left:
                temp = root.left
                while temp.right and temp.right != root:
                    temp = temp.right
                if temp.right:
                    if pre and pre.val > root.val:
                        if not first:
                            first = pre
                            second = root
                        else:
                            second = root
                    pre = root
                    temp.right = None
                    root = root.right
                else:
                    temp.right = root
                    root = root.left
            else:
                if pre and pre.val > root.val:
                    if not first:
                        first = pre
                        second = root
                    else:
                        second = root
                pre = root
                root = root.right
        first.val, second.val = second.val, first.val