LeetCode - Validate Binary Search Tree

Question Definition

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

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

    1
   / \
  2   3

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

Java Solution

public boolean isValidBST(TreeNode root) {
    return isValidBST(root, Long.MIN_VALUE, Long.MAX_VALUE);
}

private boolean isValidBST(TreeNode root, long left, long right) {
    if(root == null) return true;
    if(root.val <= left || root.val >= right) return false;
    if(root.left == null && root.right == null){
        return true;
    }
    return isValidBST(root.left, left, root.val) && isValidBST(root.right, root.val, right);
}