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This article introduces you how to verify the binary search tree in python, the content is very detailed, interested friends can refer to, hope to be helpful to you.

Given a binary tree, determine whether it is a valid binary search tree.

Suppose a binary search tree has the following characteristics:

The left subtree of a node contains only a number less than the current node.

The right subtree of a node contains only a number greater than the current node.

All left and right subtrees must also be binary search trees themselves.

Example 1:

Enter:

two

/\

1 3

Output: true

Example 2:

Enter:

five

/\

1 4

/\

3 6

Output: false

Explanation: the input is: [5pr 1pr 4pr nullpr nullpr 3pr 6].

The root node has a value of 5, but its right child node has a value of 4.

Ideas for solving the problem:

1, traversal in the middle order

/ * Definition for a binary tree node. * type TreeNode struct {* Val int * Left * TreeNode * Right * TreeNode * * / var last= ^ (int (^ uint (0) > > 1) func isValidBST (root * TreeNode) bool {if rootworthy ValidBST (root.Left) {return false} if last > = root.Val {return false} last=root.Val ifValidBST ( Root.Right) {return false}} return true}

Method 2:

Recursion: the root node > is greater than the maximum value of the left node and less than the minimum value of the right node

/ * Definition for a binary tree node. * type TreeNode struct {* Val int * Left * TreeNode * Right * TreeNode * * / func isValidBST (root * TreeNode) bool {if root==nil {return true} if root.LeftExpenditure return isValidBST (root.Left) & & isValidBST (root.Right) & & l

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