Two islanders and truthfulness

What this logic-puzzle interview question tests

This is an easy logic puzzle of the kind used to warm up candidates and assess foundational reasoning under constraints. It requires you to work through a system of logical statements where each person is bound by a fixed rule—one always tells the truth, the other always lies—and derive what must be true about their identities.

The approach is systematic: assume each possible configuration, check whether the statements made by both parties are consistent with their claimed or implied types, and eliminate contradictions. Interviewers use these problems to see whether you reason carefully, check your work, and can explain your logic clearly rather than guess.

• Proof by contradiction
• Consistency of logical statements
• Working backward from constraints