Apple·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

May 2026

Summary

Apple SWE interview with a library design question that looked deceptively simple on the surface. The card deck problem packed in a lot more than I expected once they started asking about bias guarantees and complexity.

Questions Asked (1)

Design a playing-card deck library with two methods: shuffle(), which returns a uniformly random permutation of a standard 52-card deck, and order(), which returns the cards sorted by rank then suit (using the ordering Clubs, Diamonds, Hearts, Spades within each rank, starting from 3 up through Ace). Define your data structures, explain how you guarantee an unbiased shuffle, and analyze time and space complexity.

Algorithms & Data StructuresSystem DesignTechnical Trade-offs

Author's notes

I started with the data structure and defined a Card as a pair of rank and suit enums, deck as a fixed array of 52.

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AI HintsAI Generated

Suggested Approach

Start by defining a clear data structure for a card (rank and suit) and the deck (array of 52 cards). Explain the Fisher-Yates shuffle algorithm to guarantee uniformity, then describe sorting for order() using a comparator that encodes the specified rank and suit ordering. Conclude with time and space complexity analysis for both methods.

Pro tip: Mention that using a naive shuffle (like assigning random numbers to each card and sorting) can introduce bias, and that Fisher-Yates is the industry standard for unbiased shuffling. Also, note that the order() method could be implemented by sorting a copy of the deck, but if the deck is already in order, you might return a new sorted array to avoid mutating the original.

1. Define Data Structures

Represent a card as a struct or class with rank (3-15, where 11=Jack, 12=Queen, 13=King, 14=Ace) and suit (0=Clubs, 1=Diamonds, 2=Hearts, 3=Spades). The deck is an array or list of 52 such cards.

2. Implement shuffle() with Fisher-Yates

Iterate from the last index down to 1, swap the current card with a randomly chosen card from the remaining unshuffled portion (indices 0 to i). This ensures each permutation is equally likely.

3. Implement order() with Custom Comparator

Sort the deck using a comparator that first compares ranks (3 to Ace) and then suits in the order Clubs, Diamonds, Hearts, Spades. Return a new sorted array to avoid mutating the original deck.

4. Analyze Complexity

shuffle() runs in O(n) time and O(1) extra space (in-place). order() runs in O(n log n) time due to sorting and O(n) space if creating a new array, or O(1) if sorting in-place.

5. Discuss Trade-offs and Edge Cases

Consider whether shuffle() should mutate the deck or return a new shuffled deck. Discuss the importance of a good random number generator and potential biases if not using Fisher-Yates.

Key Points to Mention

Fisher-Yates shuffle algorithm and its unbiased nature
Custom comparator for sorting by rank then suit with specified suit order
Time complexity: O(n) for shuffle, O(n log n) for order
Space complexity: O(1) for in-place shuffle, O(n) for sorted copy
Avoiding bias in shuffle by not using naive random sort
Immutability considerations: whether methods mutate the deck or return new arrays

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