[LeetCode] 0098 Validate Binary Search Tree

Validate Binary Search Tree

LeetCode - 0098 Validate Binary Search Tree
https://leetcode.com/problems/validate-binary-search-tree/

Problem 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