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Blue-Eyed Islanders
This Hard puzzle in the “logic” category rewards careful reading and step-by-step reasoning. Use the hint if you are stuck, then compare your approach with the explained answer.
On an island, every person can see everyone else’s eye color, but no one knows their own eye color.
No one may discuss eye color.
There is a rule: if a person ever knows for certain that they have blue eyes, they must leave the island that night.
One day, a visitor says publicly: “At least one of you has blue eyes.”
Suppose exactly 100 people on the island have blue eyes.
What happens?
Preparing…