问题：

给定数据结构.png

题目要求.png

思路：

在给定数据结构的基础上，自定义一个数据结构，包装给定的数据结构，再加一个count计数，不管加入的是狗还是猫，count都++，输出整个队列的时候，只需要比较猫狗队列的队列顶count的大小，小的先输出。

代码：

public static class Pet {
        private String type;

        public Pet(String type) {
            this.type = type;
        }

        public String getPetType() {
            return this.type;
        }
    }

    public static class Dog extends Pet {
        public Dog() {
            super("dog");
        }
    }

    public static class Cat extends Pet {
        public Cat() {
            super("cat");
        }
    }

    public static class PetEnterQueue {
        private Pet pet;
        private long count;

        public PetEnterQueue(Pet pet, long count) {
            this.pet = pet;
            this.count = count;
        }

        public Pet getPet() {
            return this.pet;
        }

        public long getCount() {
            return this.count;
        }

        public String getEnterPetType() {
            return this.pet.getPetType();
        }
    }

    public static class DogCatQueue {
        private Queue<PetEnterQueue> dogQ;
        private Queue<PetEnterQueue> catQ;
        private long count;

        public DogCatQueue() {
            this.dogQ = new LinkedList<PetEnterQueue>();
            this.catQ = new LinkedList<PetEnterQueue>();
            this.count = 0;
        }

        public void add(Pet pet) {
            if (pet.getPetType().equals("dog")) {
                this.dogQ.add(new PetEnterQueue(pet, this.count++));
            } else if (pet.getPetType().equals("cat")) {
                this.catQ.add(new PetEnterQueue(pet, this.count++));
            } else {
                throw new RuntimeException("err, not dog or cat");
            }
        }

        public Pet pollAll() {
            if (!this.dogQ.isEmpty() && !this.catQ.isEmpty()) {
                if (this.dogQ.peek().getCount() < this.catQ.peek().getCount()) {
                    return this.dogQ.poll().getPet();
                } else {
                    return this.catQ.poll().getPet();
                }
            } else if (!this.dogQ.isEmpty()) {
                return this.dogQ.poll().getPet();
            } else if (!this.catQ.isEmpty()) {
                return this.catQ.poll().getPet();
            } else {
                throw new RuntimeException("err, queue is empty!");
            }
        }

        public Dog pollDog() {
            if (!this.isDogQueueEmpty()) {
                return (Dog) this.dogQ.poll().getPet();
            } else {
                throw new RuntimeException("Dog queue is empty!");
            }
        }

        public Cat pollCat() {
            if (!this.isCatQueueEmpty()) {
                return (Cat) this.catQ.poll().getPet();
            } else
                throw new RuntimeException("Cat queue is empty!");
        }

        public boolean isEmpty() {
            return this.dogQ.isEmpty() && this.catQ.isEmpty();
        }

        public boolean isDogQueueEmpty() {
            return this.dogQ.isEmpty();
        }

        public boolean isCatQueueEmpty() {
            return this.catQ.isEmpty();
        }

    }