SIG (Susquehanna)·Data Scientist·Technical Phone Screen·Intermediate

Intermediate

Jun 2026

Summary

SIG logic puzzle interview for a Data Scientist role. One question, four variants, and the kind of problem that sounds like a riddle from a philosophy class. Pretty classic for a quant-adjacent shop.

Questions Asked (1)

On an island of knights (always truthful) and knaves (always lying), person B says to A: 'You always lie,' and then makes a second claim. There are four possible second claims: (1) A is a knave and B is a knight, (2) A is a knight and B is a knave, (3) A is a knave and B is a knave, (4) A is a knight and B is a knight. For each variant, determine the consistent identities of A and B, or state that no consistent solution exists.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

This wrecked me a little.

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AI HintsAI Generated

Suggested Approach

Model each person's type as a boolean (knight = true) and translate each statement into a logical constraint. For each variant, solve the resulting system of equations by case analysis or truth table, checking consistency with the knights-and-knaves rules.

Pro tip: Clearly state your assumptions and walk through the logic step-by-step; interviewers value structured reasoning over just the final answer, especially for puzzles that test algorithmic thinking.

1. Define variables and truth conditions

Let A and B be booleans where true means knight (truth-teller) and false means knave (liar). A statement made by a person is true if and only if that person is a knight.

2. Translate B's first statement

B says 'A always lies', which means A is a knave (A = false). So the truth value of this statement is (not A). Since B made the statement, we have B = (not A).

3. Translate the second claim for each variant

For each of the four second claims, express the claim as a logical formula involving A and B, then set B equal to the truth value of that formula (since B is the speaker).

4. Solve the system for each variant

Combine the equation from step 2 with the equation from step 3 for each variant. Solve for A and B, and check if the solution satisfies all constraints (i.e., no contradiction).

5. State the consistent identities or no solution

For each variant, report whether a consistent assignment exists and what it is (e.g., A is a knight, B is a knave). If no assignment satisfies both equations, state that no consistent solution exists.

Key Points to Mention

Boolean representation: knight = true, knave = false.
The rule: a person's statement is true iff they are a knight.
B's first statement 'A always lies' is equivalent to 'A is a knave'.
Systematic case analysis or truth table for each variant.
Checking for contradictions: if the derived identities conflict with the assumption, no solution.
Clear communication of the final answer for each variant.

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