BST Verification | Dataford Interview Questions

Verify if a given binary tree is a BST. Duplicate values appear towards the left.

Asked in the phone interview stage. This was the first question.

Input and Output

Implement def is_bst(root):. Each node is a dictionary with keys val, left, and right, or null. Return true if every left-subtree value is less than or equal to its ancestor and every right-subtree value is strictly greater; otherwise return false.

Constraints

The tree contains at most 500 nodes
Each node value is an integer
The input uses null for an absent child
Equal values may appear in a left subtree but not in a right subtree

Function Signature

def is_bst(root):

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