Validate linked list balanced
Last updated: July 16, 2025
Quick Overview
Given a linked list, write a function to determine if it is balanced, meaning that the number of nodes in the left half of the list is equal to the number of nodes in the right half. The function should return a boolean value: `true` if the linked list is balanced and `false` otherwise. The input will be the head node of the linked list.
HubSpot
July 16, 202525
12
3,003 solved
Given a linked list, write a function to determine if it is balanced, meaning that the number of nodes in the left half of the list is equal to the number of nodes in the right half. The function should return a boolean value: `true` if the linked list is balanced and `false` otherwise. The input will be the head node of the linked list.
HubSpot uses this problem in the Technical Screen to evaluate your algorithmic thinking. They expect you to discuss multiple approaches, analyze trade-offs between them, and implement the optimal solution with clean, readable code.
What the Interviewer Expects
- Recognize the underlying problem pattern (sliding window, two pointers, BFS/DFS, etc.)
- Discuss multiple approaches and trade-offs before coding
- Implement an optimal solution with clean, production-quality code
- Handle all edge cases including boundary conditions and invalid input
- Optimize both time and space complexity with clear justification
- Test your solution systematically with well-chosen examples
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
- Can you solve this in a single pass?
- Can you optimize the space complexity of your solution?
- How would you test this solution thoroughly?
- How would your solution change if the input was sorted?
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Problem Analysis
The problem requires us to determine whether a linked list is balanced, meaning that the number of nodes in the left half of the list equals the number of nodes in the right half. This problem can be ...
Approach
- Initialize two pointers:
slowandfast. Both will start at the head of the linked list. - Traverse the linked list using a loop:
- Move the
slowpointer one step forward. - Move the `...
- Move the
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