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Grokking the Coding Interview Patterns in Python

Solution: Validate Binary Search Tree

Explore how to validate a binary search tree by using in-order traversal. Understand how tracking the previous node’s value ensures the BST property is maintained. This lesson helps you implement a recursive approach to verify that all node values follow BST rules efficiently.

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Statement

Given the root of a binary tree, check whether it is a valid binary search tree (BST).

A binary tree is a valid BST if for every node:

  • 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 are valid BSTs.

Constraints:

  • ...