[Leetcode] Validate Binary Search Tree

Problem

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.

Algorithm

Pass the [min,  max] range that the tree should fall in from root to each node. If any node falls out of the passed range, return false. Else return true. 

Code