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Pinduoduo·Software Engineer·Online Assessment (OA)·Intermediate

Intermediate
Jun 2026

Summary

Pinduoduo SWE coding round with a card/poker logic problem. Pretty niche constraint handling required, not your typical leetcode grind.

Questions Asked (1)

Q1

Given 4 characters representing card ranks from an incomplete 5-card straight (one rank missing), find and return the missing rank. Aces can be low (A-2-3-4-5) or high (above King), and each rank is encoded as a single character where Ace is '0', 10 is 'T', and face cards are their initials.

Algorithms & Data StructuresTechnical Trade-offs
Author's notes

The encoding tripped me up more than the actual logic.

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AI HintsAI Generated

Suggested Approach

First, map the character ranks to numeric values, handling the special cases of Ace as both 1 and 14. Then, sort the four values and check for the missing rank by examining gaps, including the wrap-around case for the wheel (A-2-3-4-5). Finally, return the character corresponding to the missing rank.

Pro tip: Clarify with the interviewer whether the input is guaranteed to be a valid incomplete straight and whether the missing rank could be the Ace in either position. This shows attention to edge cases and avoids incorrect assumptions.

1. Understand the encoding and straight rules

Map each character to its numeric value: '0' for Ace (1 or 14), '2'-'9' for 2-9, 'T' for 10, 'J' for 11, 'Q' for 12, 'K' for 13. Recognize that a straight consists of 5 consecutive ranks, with Ace allowed at both ends.

2. Convert and sort the given ranks

Convert the four input characters to their numeric values, treating Ace as 1 initially. Sort the resulting numbers to easily identify gaps.

3. Identify the missing rank

Check for a single gap between consecutive sorted numbers. If no gap is found, the missing rank must be at one of the ends: either 1 (Ace low) or 14 (Ace high). Handle the wheel case (A-2-3-4-5) by considering Ace as 1 and checking if the set is {1,2,3,4,5} missing one.

4. Handle Ace as high

If the sorted numbers are 10,11,12,13 (T,J,Q,K), the missing rank is Ace high (14). Also, if the sorted numbers include 1 and the gap suggests Ace high, adjust accordingly.

5. Return the missing rank as a character

Convert the missing numeric value back to its character representation: 1 or 14 -> '0', 10 -> 'T', 11 -> 'J', 12 -> 'Q', 13 -> 'K', and 2-9 as themselves.

Key Points to Mention

  • Mapping between character encoding and numeric rank values, including special cases for Ace and 10.
  • Handling Ace as both low (1) and high (14) in straight sequences.
  • Sorting the four ranks to simplify gap detection.
  • Considering the wheel straight (A-2-3-4-5) as a special case.
  • Edge cases: missing Ace low, missing Ace high, and missing middle card.
  • Time and space complexity: O(1) since only four elements are processed.

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