Apple·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Jul 2026

Summary

Got a coding question for an Analytics Engineer role at Apple that was more Python OOP than I expected. The problem wasn't crazy hard but the constraints tripped me up a bit.

Questions Asked (1)

Given a Parent class that precomputes a frequency dictionary from a list, implement a `most_frequent_key()` method in a Child subclass that returns all keys tied for the highest frequency, in order of first appearance, without using `max()` or `collections.Counter`.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

The no-`max()` constraint is what got me thinking for a second.

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AI HintsAI Generated

Suggested Approach

First, clarify the problem constraints and the parent class's precomputed frequency dictionary. Then, design a single-pass algorithm that tracks the maximum frequency and collects keys in order of first appearance, using the parent's frequency data and the original list order. Finally, discuss trade-offs and edge cases.

Pro tip: Mention that you would leverage the parent's precomputed frequency dictionary to avoid recomputation, but also note that you need the original list to determine order of first appearance. This shows you understand inheritance and data dependencies.

1. Clarify requirements and constraints

Confirm that the parent class provides a frequency dictionary and that the original list is accessible. Ensure you understand that 'order of first appearance' means the order in which keys first occur in the original list.

2. Design the algorithm

Plan a single pass over the original list: maintain a set of seen keys, track the current maximum frequency, and collect keys that achieve this maximum. Alternatively, first find the maximum frequency by iterating over the frequency dictionary, then collect keys with that frequency in order of first appearance.

3. Implement without max() or Counter

Write code that manually compares frequencies to find the maximum, and uses a list or ordered structure to preserve first-appearance order. Avoid built-in functions that directly solve the problem.

4. Test with edge cases

Consider empty list, all unique elements, all same frequency, and ties. Verify that the output order matches first appearance in the original list.

5. Discuss trade-offs and optimizations

Talk about time and space complexity: O(n) time and O(k) space where k is number of unique keys. Mention that using the parent's frequency dictionary saves recomputation, but iterating the original list is necessary for order.

Key Points to Mention

Leveraging the parent class's precomputed frequency dictionary to avoid redundant work.
The need to access the original list to determine order of first appearance.
Manual tracking of maximum frequency without using max().
Using a set or similar structure to track seen keys for order preservation.
Handling edge cases such as empty input or all keys tied.
Time and space complexity analysis and potential optimizations.

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