Constraint models for Klondike

Klondike is the most famous single-player card game, and remains a challenging search problem even in the “thoughtful” variant where all card locations are known. We consider the full game of Klondike except for one restriction that the unusual move of “worrying back” is disallowed. This model is able to determine the winnability of all instances of the game and in practice does so in less than 2000 secs for 10,000 instances we tested, which no other known algorithm can achieve. On some instances, however, other techniques can produce answers more quickly. We use constraint modelling to produce schedules for running our constraint model in combination with other techniques. The combination outperforms any single solver across a range of time limits. Using this combination we are able to significantly improve the best estimate of winnability of Klondike without worrying back. Finally we show how we can use this work to also improve the estimate of winnability of the regular game of Klondike.