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BitKernel·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
May 2026

Summary

Interviewed for a Software Engineer role at Bitkernel and ran into a logic puzzle that looked deceptively simple. One question, four cups, and I definitely second-guessed myself more than once.

Questions Asked (1)

Q1

Four cups sit on a table, each with a statement: Cup 1 says all cups contain fruit candy. Cup 2 says it contains apples. Cup 3 says it does not contain chocolate. Cup 4 says some cups do not contain fruit candy. Exactly one statement is true. Which must be true: (A) all cups have fruit candy, (B) no cup has fruit candy, (C) no cup has apples, or (D) the third cup contains chocolate?

Algorithms & Data Structures
Author's notes

I spent way too long on this.

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AI HintsAI Generated

Suggested Approach

Treat each cup's statement as a logical proposition and systematically test each answer choice by checking consistency with the condition that exactly one statement is true. Use a truth table or case analysis to eliminate options that lead to contradictions, then verify which option must hold in all valid scenarios.

Pro tip: In logic puzzles, pay close attention to quantifiers and negations—statements 1 and 4 are direct contradictions, so exactly one of them must be true; this immediately constrains the other statements to be false, simplifying the analysis.

1. Formalize the statements

Translate each cup's statement into precise logical notation, identifying the domain (cups) and predicates (contains fruit candy, contains apples, contains chocolate).

2. Identify logical relationships

Note that Cup 1 (all cups have fruit candy) and Cup 4 (some cups do not have fruit candy) are negations of each other, so exactly one of them is true.

3. Apply the exactly-one-true constraint

Since one of Cup 1 or Cup 4 is true, the other must be false, and Cups 2 and 3 must also be false. This yields: Cup 2 does not contain apples, and Cup 3 contains chocolate.

4. Evaluate each answer choice

Check which option is necessarily true given the derived facts: Cup 3 contains chocolate is directly forced, while the others are not guaranteed (e.g., all cups could have fruit candy or not).

5. Confirm with a counterexample check

For each incorrect option, construct a valid scenario where it is false to ensure only the chosen option must be true.

Key Points to Mention

  • Logical negation and contradiction between universal and existential statements
  • Case analysis or truth table method for exactly-one-true constraints
  • Quantifiers: 'all' vs. 'some' and their negations
  • Deriving forced conclusions from false statements (e.g., false 'contains apples' means 'does not contain apples')
  • Verification by counterexample for answer choices
  • Systematic elimination of options that are not necessarily true

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