LeetCode 0098  Validate Binary Search Tree
Validate Binary Search Tree
Desicription
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:


Binary tree [2,1,3]
, return true.
Example 2:


Binary tree [1,2,3]
, return false.
Solution

