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Grokking the Coding Interview Patterns

Solution: Validate Binary Search Tree

Understand how to determine if a binary tree is a valid binary search tree by performing an in-order traversal and ensuring the node values strictly increase. This lesson guides you through the validation algorithm, explains its time and space complexities, and offers practical insight to apply in coding interviews.

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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:

  • ...