Turning down one or two adjacent cards in a row of ten
Question
Ten cards lie face up in a line. Two players alternate turns. On the very first move, the first player must turn exactly one card face down. Thereafter, on each turn a player turns face down either one face-up card or two face-up cards that are next to each other. The player who turns down the final card wins. With best play, who wins? Answer for the first player, for the second.
Short answer
(the first player). For instance, turning down the third card from an end splits the row into piles of and ; this is the game Kayles and the Sprague-Grundy values of these piles cancel (), so the first player can keep returning a zero position, e.g. by mirroring across symmetric sub-rows, and takes the last card.
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Open the worked solutionLessons behind this question
- Sample Spaces, Events, and the Probability Axioms
- Conditional Probability, Total Probability, and Bayes' Rule
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