99. 恢复二叉搜索树.py

# 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.
        """
        '''
        #中序遍历 迭代
        firstNode = None
        secondNode = None
        pre = TreeNode(float("-inf"))

        stack = []
        p = root
        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:
                #print(firstNode.val,pre.val, p.val)
                secondNode = p
            pre = p
            p = p.right
        firstNode.val, secondNode.val = secondNode.val, firstNode.val
        '''
        # 中序遍历 递归
        self.firstNode = None
        self.secondNode = None
        self.preNode = TreeNode(float("-inf"))

        def in_order(root):
            if not root:
                return
            in_order(root.left)
            if self.firstNode == None and self.preNode.val >= root.val:
                self.firstNode = self.preNode
            if self.firstNode and self.preNode.val >= root.val:
                self.secondNode = root
            self.preNode = root
            in_order(root.right)

        in_order(root)
        self.firstNode.val, self.secondNode.val = self.secondNode.val, self.firstNode.val