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Pinduoduo·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say
Apr 2026

Summary

Pinduoduo SWE interview with a card game algorithm problem. Nothing too wild but the edge cases kept me on my toes longer than I'd like to admit.

Questions Asked (1)

Q1

Given a collection of poker cards, write a function to detect whether a Straight Flush exists (5 cards of the same suit with consecutive ranks). Handle the Ace as both high and low.

Algorithms & Data Structures
Author's notes

The grouping by suit part came naturally, sorting ranks too.

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AI HintsAI Generated

Suggested Approach

Group cards by suit, then for each suit, extract ranks and check for 5 consecutive ranks. Handle Ace as both high (14) and low (1) by considering both possibilities in the rank set.

Pro tip: Clarify input format and edge cases (e.g., duplicates, jokers) before coding, and mention that the algorithm runs in O(n) time with O(n) space, which is optimal.

1. Clarify requirements and edge cases

Ask about input representation (e.g., list of strings or objects), whether duplicates are possible, and if Ace can be used as both high and low simultaneously (it cannot).

2. Group cards by suit

Iterate through the collection and build a map from suit to a set of ranks, ignoring duplicates or handling them appropriately.

3. Check each suit for consecutive ranks

For each suit's rank set, sort the ranks and check for any sequence of 5 consecutive values. Also handle Ace by adding 14 (if Ace present) and checking for sequences involving 1 (Ace low) and 14 (Ace high).

4. Return result and discuss complexity

Return true if any suit has a straight flush, else false. Analyze time and space complexity, noting O(n) time and O(n) space.

Key Points to Mention

  • Grouping by suit to reduce problem to checking consecutive ranks per suit.
  • Handling Ace as both high (14) and low (1) by considering both values in the rank set.
  • Using a set for ranks to eliminate duplicates and enable O(1) lookups.
  • Checking for 5 consecutive ranks efficiently, e.g., by sorting or using a sliding window.
  • Time complexity: O(n) where n is number of cards, space complexity: O(n).
  • Edge cases: fewer than 5 cards, multiple suits, Ace-low straight (A-2-3-4-5), Ace-high straight (10-J-Q-K-A).

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