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Pinduoduo·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say
May 2026

Summary

Coding round at Pinduoduo for a software engineer role. The main problem was about detecting a straight flush in a hand of cards, which sounds simple enough until you actually sit down and think through all the edge cases.

Questions Asked (1)

Q1

Given a list of playing cards, determine whether any five cards of the same suit have consecutive ranks forming a straight flush. Return those five cards if found, otherwise return false.

Algorithms & Data Structures
Author's notes

The core logic isn't bad once you bucket by suit and sort.

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AI HintsAI Generated

Suggested Approach

Group the cards by suit, then for each suit, extract the ranks, sort them, and check for any sequence of five consecutive ranks. If found, return the corresponding cards; otherwise, return false. Discuss handling duplicates and edge cases like Ace-low straights.

Pro tip: Clarify upfront whether Ace can be low (A-2-3-4-5) and whether duplicate ranks are allowed, as these assumptions affect the algorithm. Mentioning this shows attention to detail and prevents incorrect solutions.

1. Clarify requirements and edge cases

Ask about Ace's role (high, low, or both), duplicate cards, and whether the five cards must be distinct. Confirm input format and expected output.

2. Group cards by suit

Iterate through the list and build a map from suit to a list of ranks (or cards). This reduces the problem to checking each suit independently.

3. Check for consecutive ranks per suit

For each suit, sort the unique ranks and scan for a run of five consecutive values. Handle Ace-low by treating Ace as 1 if needed.

4. Return the result

If a straight flush is found, return the five cards (e.g., as a list). If no suit qualifies, return false.

Key Points to Mention

  • Time and space complexity: O(n log n) due to sorting, or O(n) with counting sort if ranks are bounded.
  • Handling Ace as both high and low (e.g., A-2-3-4-5 and 10-J-Q-K-A).
  • Dealing with duplicate ranks: ensure five distinct consecutive ranks.
  • Edge cases: fewer than five cards, multiple suits with straight flushes (return any one), and no straight flush.
  • Choice of data structures: hash map for grouping, set for uniqueness, or bitmask for efficiency.
  • Testing strategy: include cases with Ace-low, duplicates, and multiple suits.

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