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Sig·Software Engineer·Technical Phone Screen·Junior

Junior
Jul 2026

Summary

SIG quant engineer interview with a classic knights and knaves logic puzzle. Short and sharp, felt more like a screening than a deep technical round.

Questions Asked (1)

Q1

On an island where knights always tell the truth and knaves always lie, person B makes two statements: 'A and I are the same type' and 'A always lies.' What type is each person?

Algorithms & Data StructuresTechnical Trade-offs
Author's notes

I stared at this for a second because both statements together create a contradiction if you assume B is a knight.

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AI HintsAI Generated

Suggested Approach

Treat each person's type as a boolean variable (knight = true, knave = false) and translate the statements into logical constraints. Systematically test both possible types for A and check consistency with B's truthfulness and the content of B's statements.

Pro tip: After finding a consistent assignment, briefly verify that the other assignment leads to a contradiction, demonstrating thoroughness and logical rigor.

1. Define variables and truth conditions

Let A and B represent whether each is a knight (true) or knave (false). Recall that a knight's statements are true and a knave's statements are false.

2. Translate B's statements into logical constraints

B says: (1) 'A and I are the same type' → A = B. (2) 'A always lies' → A is a knave (A = false).

3. Case analysis on B's type

If B is a knight, both statements must be true: A = B and A = false. Since B = true, A = true from the first, but A = false from the second → contradiction. If B is a knave, both statements must be false: A ≠ B and A ≠ false (i.e., A = true). Since B = false, A ≠ false means A = true, which also satisfies A ≠ B. Consistent.

4. Determine types and verify

The only consistent assignment is A = knight (true) and B = knave (false). Verify: B's first statement 'A and I are the same type' is false (they are different), and second statement 'A always lies' is false (A is a knight). Both false, as required for a knave.

Key Points to Mention

  • Knights always tell the truth; knaves always lie.
  • Represent types as booleans: knight = true, knave = false.
  • Translate each statement into a logical equation.
  • Use case analysis on B's type to find consistency.
  • Check for contradictions in each case.
  • Verify the final assignment satisfies all conditions.

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