AnimalShelter.java

package algorithm.cracking.stacks;

import lombok.Getter;
import lombok.NoArgsConstructor;
import lombok.ToString;
import lombok.experimental.SuperBuilder;

import java.time.LocalDateTime;
import java.util.LinkedList;
import java.util.Optional;
import java.util.Queue;

/**
 * An animal shelter, which holds only dogs and cats, operates on a strictly "first in, first out" basis.
 * People must adopt either the "oldest" (based on arrival time) of all animals at the shelter,
 * or they can select whether they would prefer a dog or a cat (and will receive the oldest animal of
 * that type). They cannot select which specific animal they would like. Create the data structures to
 * maintain this system and implement operations such as enqueue, dequeueAny, dequeueDog,
 * and dequeueCat. You may use the built-in Linkedlist data structure.
 */
public class AnimalShelter {

    Queue<Dog> queueDogs = new LinkedList<>();
    Queue<Cat> queueCats = new LinkedList<>();

    void enqueue(Animal animal) {
        if (animal instanceof Dog dog) queueDogs.offer(dog);
        else if (animal instanceof Cat cat) queueCats.offer(cat);
        else throw new RuntimeException("Unsupported animal");
    }

    Optional<?> dequeueAny() {
        if (queueDogs.isEmpty()) return dequeueCat();
        if (queueCats.isEmpty()) return dequeueDog();

        var oldDog = queueDogs.peek();
        var oldCat = queueCats.peek();
        if (oldDog.getArrivalDate().isBefore(oldCat.getArrivalDate())) {
            return dequeueDog();
        } else {
            return dequeueCat();
        }
    }

    Optional<Dog> dequeueDog() {
        return Optional.ofNullable(queueDogs.poll());
    }

    Optional<Cat> dequeueCat() {
        return Optional.ofNullable(queueCats.poll());
    }


    @Getter
    @NoArgsConstructor
    @SuperBuilder
    @ToString
    abstract static class Animal {
        private String name;
        private LocalDateTime arrivalDate;
    }

    @SuperBuilder
    @Getter
    static class Dog extends Animal {
    }

    @SuperBuilder
    @Getter
    static class Cat extends Animal {
    }

}