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Section 1Understand Problem
Section 01
Understand the problem
Restate the problem precisely. Interviewers reward candidates who pause, define the contract, and name the guarantees before coding.
Problem statement
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 contains only nodes with keys greater than the node's key; both subtrees must also be binary search trees.
Example
root = [2,1,3] → true
Constraints
1 ≤ tree size ≤ 10⁴ · −2³¹ ≤ Node.val ≤ 2³¹ − 1
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WPM—Fillers0Pace—Thinking0%
Explain the problem in your own words
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AI Review
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The reviewer will check whether you stated inputs, output, guarantees, and any assumption you flagged.
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