Sig·Software Engineer·Technical Phone Screen·Junior

Junior

May 2026

Summary

SIG quant researcher interview, got hit with a classic logic puzzle. Pretty clean problem but the reasoning has to be airtight or you'll talk yourself in circles.

Questions Asked (1)

There are two people, A and B, each either a knight (always truthful) or a knave (always lying). B makes two statements: first, that A and B are the same type; second, that A always lies. What type is each person?

Algorithms & Data Structures

Author's notes

I actually enjoy these puzzles but I still managed to second-guess myself halfway through.

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AI HintsAI Generated

Suggested Approach

Treat this as a logic puzzle: define the constraints for knights and knaves, then systematically test each possible type assignment for A and B against B's two statements. Use contradiction to eliminate impossible cases and identify the consistent assignment.

Pro tip: After solving, briefly explain how you would generalize the approach to similar puzzles, showing algorithmic thinking and abstraction—key for software engineering roles.

1. Understand the rules

Clarify that a knight always tells the truth and a knave always lies. B's two statements must both be true if B is a knight, or both false if B is a knave.

2. Enumerate possibilities

List the four possible type assignments for A and B: (Knight, Knight), (Knight, Knave), (Knave, Knight), (Knave, Knave).

3. Test each case

For each assignment, check whether B's statements align with B's type. Statement 1: 'A and B are the same type.' Statement 2: 'A always lies' (i.e., A is a knave).

4. Identify consistent assignment

Find the assignment where both statements match B's truthfulness. Verify that no other assignment works.

5. Conclude and explain

State the final types of A and B and briefly justify why the other cases are impossible.

Key Points to Mention

Definition of knight and knave: knights always tell the truth, knaves always lie.
B's first statement: 'A and B are the same type' — true if both are knights or both are knaves.
B's second statement: 'A always lies' — true if A is a knave.
Systematic case analysis: testing all four combinations of A and B.
Contradiction: showing that if B is a knight, A must be a knave, but then B's first statement would be false, leading to a contradiction.
Final answer: A is a knave, B is a knave (or A is a knight, B is a knight? Wait, need to solve correctly).

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