The answers given do not take into consideration when the max min for an integer is given in the tree nor the max of an integer is given in the tree. ex. [-2147483648,null,2147483647].
Also in the description it states:
Given a Binary Tree, figure out whether it’s a Binary Search Tree. In a binary search tree, each node’s key value is smaller than the key value of all nodes in the right subtree, and are greater than the key values of all nodes in the left subtree i.e. L < N <; R.
It states that this tree does not allow duplicates but the solution given does.