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straightforward five-card poker hand comparison
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| package poker; | |
| public record Card(Rank rank, Suit suit) { | |
| public enum Rank { | |
| TWO, THREE, FOUR, FIVE, SIX, SEVEN, EIGHT, NINE, TEN, JACK, QUEEN, KING, ACE | |
| } | |
| public enum Suit { | |
| DIAMONDS, CLUBS, HEARTS, SPADES | |
| } | |
| } |
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| package poker; | |
| public enum Category { | |
| HIGH_CARD, ONE_PAIR, TWO_PAIR, THREE_OF_A_KIND, STRAIGHT, FLUSH, FULL_HOUSE, FOUR_OF_A_KIND, STRAIGHT_FLUSH | |
| } |
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| package poker; | |
| import java.util.*; // Arrays, Comparator, Set | |
| import java.util.function.Function; | |
| import poker.Card.Rank; | |
| import static java.util.Comparator.*; // comparing, naturalOrder | |
| import static java.util.stream.Collectors.*; // counting, groupingBy | |
| import static poker.Card.Rank.*; | |
| public record Hand(Category category, Rank... ranks) implements Comparable<Hand> { | |
| public static Hand evaluate(Set<Card> cards) { | |
| assert cards.size() == 5; | |
| var counts = cards.stream().collect(groupingBy(Card::rank, counting())); | |
| Function<Rank,Long> count = counts::get; | |
| var order = comparing(count).thenComparing(naturalOrder()).reversed(); | |
| Rank[] ranks = counts.keySet().stream().sorted(order).toArray(Rank[]::new); | |
| var straight = ranks[0].ordinal() - ranks[ranks.length - 1].ordinal() == 4; | |
| var wheel = ranks[0] == ACE && ranks[1] == FIVE; | |
| var flush = cards.stream().map(Card::suit).distinct().count() == 1; | |
| return counts.get(ranks[0]) == 4 ? new Hand(QUADS, ranks) | |
| : ranks.length == 2 ? new Hand(FULL_HOUSE, ranks) | |
| : counts.get(ranks[0]) == 3 ? new Hand(TRIPS, ranks) | |
| : ranks.length == 3 ? new Hand(TWO_PAIR, ranks) | |
| : ranks.length == 4 ? new Hand(PAIR, ranks) | |
| : straight ? new Hand(flush ? STRAIGHT_FLUSH : STRAIGHT, ranks[0]) | |
| : wheel ? new Hand(flush ? STRAIGHT_FLUSH : STRAIGHT, FIVE) | |
| : new Hand(flush ? FLUSH : HIGH_CARD, ranks); | |
| } | |
| @Override | |
| public int compareTo(Hand hand) { | |
| return Comparator.comparing(Hand::category) | |
| .thenComparing(Hand::ranks, Arrays::compare) | |
| .compare(this, hand); | |
| } | |
| } |
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