Validate linked list valid BST
Last updated: February 23, 2026
Quick Overview
Given a linked list where each node contains a value, determine if the values in the linked list can represent a valid binary search tree (BST). A valid BST must satisfy the property that for any given node, all values in its left subtree are less than the node's value, and all values in its right subtree are greater. Return true if the linked list can form a valid BST, and false otherwise.
Snapchat
February 23, 20261
15
4,290 solved
Given a linked list where each node contains a value, determine if the values in the linked list can represent a valid binary search tree (BST). A valid BST must satisfy the property that for any given node, all values in its left subtree are less than the node's value, and all values in its right subtree are greater. Return true if the linked list can form a valid BST, and false otherwise.
This coding problem is frequently asked during Onsite at Snapchat. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Snapchat expects candidates to write production-quality code, not just solve the puzzle.
What the Interviewer Expects
- Identify the correct data structure and algorithm for the problem
- Write clean, bug-free code with proper variable naming
- Analyze time and space complexity correctly
- Handle basic edge cases (empty input, single element)
- Communicate your thought process while coding
Key Topics to Cover
How to Approach This
- Clarify input constraints and edge cases before writing code.
- Walk through your approach verbally and confirm with the interviewer before coding.
- Start with a brute force solution, then optimize. Mention time and space complexity.
- Test your solution with examples, including edge cases like empty input or duplicates.
- Consider common patterns: sliding window, two pointers, hash map, BFS/DFS, dynamic programming.
Possible Follow-up Questions
- What if the input doesn't fit in memory?
- How would your solution change if the input was sorted?
- Can you solve this in a single pass?
- Can you solve this iteratively instead of recursively (or vice versa)?
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Problem Analysis
To determine if the values in a linked list can represent a valid BST, we need to ensure that for every element in the linked list, it can be arranged such that all elements to the left are smaller an...
Approach
- Traverse the linked list and extract all values into an array. For example, if the linked list contains values 3 -> 1 -> 4 -> 2, we will create an array [3, 1, 4, 2].
- Sort the array. After sorti...
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