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Sig·Software Engineer·Technical Phone Screen·Junior

Junior
Jun 2026

Summary

Interviewed for a quant researcher role at SIG and got hit with a classic logic puzzle. Short and focused, just the one problem but it required clean reasoning under pressure.

Questions Asked (1)

Q1

On an island where knights always tell the truth and knaves always lie, person A says 'we are both the same type' and person B says 'we are each a different type.' What type is each person?

Algorithms & Data Structures
Author's notes

The key thing I noticed pretty fast is that A and B are directly contradicting each other, so exactly one of them is telling the truth.

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AI HintsAI Generated

Suggested Approach

Treat the statements as logical constraints and test each possible assignment of types to A and B. Use case analysis or derive a contradiction to determine the unique consistent assignment.

Pro tip: After solving, briefly explain how you would generalize the approach to similar puzzles, showing algorithmic thinking and problem-solving skills.

1. Understand the rules

Knights always tell the truth; knaves always lie. Each person is exactly one type.

2. List possible assignments

There are four possibilities: both knights, both knaves, A knight and B knave, A knave and B knight.

3. Evaluate A's statement

A says 'we are both the same type.' Check if this statement is true or false for each assignment.

4. Evaluate B's statement

B says 'we are each a different type.' Check if this statement is true or false for each assignment.

5. Apply truth/lie constraints

For each assignment, ensure that if the person is a knight, their statement is true; if a knave, their statement is false. Find the consistent assignment.

Key Points to Mention

  • Logical consistency and case analysis
  • Truth-teller vs liar constraints
  • Systematic evaluation of all possibilities
  • Deriving a unique solution
  • Generalizing to similar puzzles
  • Clear communication of reasoning

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