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98. Validate Binary Search Tree

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Description

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.

 

Example 1:

    2

   / \

  1   3



Input: [2,1,3]

Output: true

Example 2:

    5

   / \

  1   4

     / \

    3   6



Input: [5,1,4,null,null,3,6]

Output: false

Explanation: The root node's value is 5 but its right child's value is 4.

Solutions

Python3

Java

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