[leetcode] Validate Binary Search Tree （检验是否为二叉查找树） Python

2019年2月25日 320次阅读 来源: zhidan

Given a binary tree, determine if it is a valid binary search tree (BST).

Assume a BST is defined as follows:

  • The left subtree of a node contains only nodes with keys less than the node’s key.
  • The right subtree of a node contains only nodes with keys greater than the node’s key.
  • Both the left and right subtrees must also be binary search trees.

leetcode已经给出了二叉查找树的定义了。

 

class Solution:
    # @param root, a tree node
    # @return a boolean
    def isValidBST(self, root):
        if root is None:
            return True
        return self.helper(root,-99999,999999)
    
    # left ~ right 是node的取值范围
    def helper(self,root,left,right):
        
        if root is None:
            return True
        if root.val <= left or root.val >=right:
            #超出范围
            return False
        return self.helper(root.left,left,root.val) and self.helper(root.right,root.val,right)

 

找到画图工具后我再来更新部分的图

 

    原文作者：zhidan
    原文地址: https://www.cnblogs.com/zhidan/p/3978648.html
    本文转自网络文章，转载此文章仅为分享知识，如有侵权，请联系博主进行删除。
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