Validate linked list complete
Last updated: February 20, 2026
Quick Overview
Given a singly linked list, write a function to determine if the linked list is complete, meaning all levels of the list are fully filled except possibly for the last level, which should be filled from left to right. The function should return a boolean value: true if the linked list is complete, and false otherwise.
Lyft
February 20, 202644
6
2,661 solved
Given a singly linked list, write a function to determine if the linked list is complete, meaning all levels of the list are fully filled except possibly for the last level, which should be filled from left to right. The function should return a boolean value: true if the linked list is complete, and false otherwise.
Coding interviews at Lyft focus on problem-solving approach as much as the final solution. The interviewer wants to see you break down the problem, consider edge cases, and optimize iteratively. Communication throughout the process is key.
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
- What happens if the input contains duplicates?
- How would you modify your solution to handle streaming input?
- What is the worst-case input for your solution?
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Problem Analysis
To determine if a singly linked list is complete, we need to understand the structure of a complete binary tree. A linked list can be represented as a binary tree where each node has at most two child...
Approach
- Initialize a queue to facilitate BFS traversal.
- Start from the head of the linked list and enqueue it.
- While the queue is not empty, dequeue a node and check its children (left and right). ...
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