Validate Binary Search Tree

MediumTreesTree

Solve this the way you would in the interview: out loud, on a timer, with an AI interviewer asking follow-ups while you code. You get a scored report at the end.

Practice this as a mock interviewFree to start, no account needed

Problem

Given the root of a binary tree, determine if it is a valid binary search tree (BST). A valid 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.

Examples

Input: root = [2,1,3]
Output: true
Input: root = [5,1,4,null,null,3,6]
Output: false
The root node's value is 5 but its right child's value is 4.

Constraints

  • The number of nodes in the tree is in the range [1, 10^4].
  • -2^31 <= Node.val <= 2^31 - 1

What the interviewer grades

A correct solution is one of five scores. The report also grades problem understanding (did you clarify inputs and edge cases before coding), problem solving, communication while you work, code quality, and testing. See a sample report, or read up on the pattern in the lessons.

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