Meta·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Jun 2026

Summary

Meta SWE interview with a classic linked list problem. Not much to say, it was pretty standard.

Questions Asked (1)

Merge two sorted linked lists into a single sorted list.

Algorithms & Data Structures

Author's notes

Pretty much a bread-and-butter problem.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the problem (e.g., whether the lists are singly linked, sorted in ascending order, and if we can modify the input lists). Then, propose an iterative two-pointer approach with a dummy head to merge the lists in O(n+m) time and O(1) space, and walk through a small example to illustrate. Finally, discuss edge cases and potential optimizations or alternatives like recursion.

Pro tip: Emphasize the dummy head technique to simplify edge cases and avoid special handling for the first node. Also, mention that you would write clean, modular code with meaningful variable names and test it with edge cases like empty lists and lists of different lengths.

1. Clarify requirements and constraints

Ask about the linked list structure (singly/doubly), sorting order, whether input lists can be modified, and if there are memory constraints. Confirm the expected time and space complexity.

2. Outline the approach

Explain that you will use two pointers to traverse the lists, compare nodes, and build the merged list using a dummy head to simplify insertion. Mention that this achieves O(n+m) time and O(1) space.

3. Walk through an example

Choose a simple example (e.g., 1->3->5 and 2->4->6) and step through the algorithm, showing how pointers advance and nodes are linked. This demonstrates understanding and catches off-by-one errors.

4. Discuss edge cases and complexity

Cover cases like one or both lists empty, lists of different lengths, duplicate values, and negative numbers. Reiterate time and space complexity and why it's optimal.

5. Code and test

Write clean code with clear variable names, then mentally test with the example and edge cases. If time permits, mention alternative recursive solution and its trade-offs.

Key Points to Mention

Use of a dummy head node to simplify edge cases and avoid special handling for the first node.
Two-pointer technique to traverse both lists simultaneously, comparing and advancing the pointer of the smaller node.
Time complexity O(n+m) and space complexity O(1) for the iterative solution.
Handling of edge cases: empty lists, lists of different lengths, duplicate values, and negative numbers.
Ability to modify input lists (if allowed) to avoid extra space, otherwise discuss creating a new list.
Potential recursive solution and its O(n+m) space complexity due to call stack, contrasting with iterative approach.

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