Confluent·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Jun 2026

Summary

Confluent software engineer interview with a linked list problem that sounds easy until you actually have to implement it cleanly under pressure.

Questions Asked (1)

Given the head of a singly linked list and an integer n, return the nth node from the end of the list. Solve it in a single pass.

Algorithms & Data Structures

Author's notes

Two pointers, advance the fast one n steps, then walk both until fast hits null.

Create a free account to read the full note

AI HintsAI Generated

Suggested Approach

Use the two-pointer technique: advance the first pointer n nodes ahead, then move both pointers until the first reaches the end. The second pointer will then be at the nth node from the end. This achieves a single pass with O(n) time and O(1) space.

Pro tip: Clarify edge cases upfront (e.g., n larger than list length, n=1, empty list) and discuss how to handle them, showing attention to detail. Also, mention that the two-pointer approach is optimal and commonly expected in interviews.

1. Understand the problem and edge cases

Confirm the definition of 'nth from the end' (1-indexed) and consider edge cases: empty list, n <= 0, n > length. Discuss how to handle these (e.g., return null or throw exception).

2. Design the two-pointer approach

Initialize two pointers (first and second) at the head. Move first n nodes ahead. If first becomes null before n steps, n is larger than the list length; handle accordingly.

3. Traverse with both pointers

While first is not null, move both pointers one step at a time. When first reaches the end (null), second will be at the nth node from the end.

4. Return the result and verify

Return the second pointer (or its value). Walk through a small example to verify correctness, and state the time and space complexity: O(n) time, O(1) space.

Key Points to Mention

Two-pointer technique (fast and slow pointers)
Single pass requirement and how it's achieved
Time complexity: O(n), Space complexity: O(1)
Edge case handling: n > list length, n = 1, empty list
Comparison with alternative approaches (e.g., two passes or using a stack)
Potential follow-up: what if the list is circular? (discuss cycle detection)

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.