Abstract
Consider the following one player game. A deck containing m copies of n different card types is shuffled uniformly at random. Each round the player tries to guess the next card in the deck, and then the card is revealed and discarded. It was shown by Diaconis, Graham, He, and Spiro that if m is fixed, then the maximum expected number of correct guesses that the player can achieve is asymptotic to , where is the mth harmonic number.
In this paper we consider an adversarial version of this game where a second player shuffles the deck according to some (possibly non-uniform) distribution. We prove that a certain greedy strategy for the shuffler is the unique optimal strategy in this game, and that the guesser can achieve at most expected correct guesses asymptotically for fixed m against this greedy strategy..
Funding Statement
This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1650112.
Acknowledgments
The author would like to thank Jimmy He for pointing out minor typos in an earlier draft, as well as the anonymous referee who offered a number of useful suggestions.
Citation
Sam Spiro. "Online card games." Electron. J. Probab. 27 1 - 15, 2022. https://doi.org/10.1214/22-EJP768
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