题目
宠物、狗和猫的类如下:
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| public class Pet {
private String type;
public Pet(String type) {
this.type = type;
}
public String getPetType() {
return this.type;
}
}
public class Dog extends Pet {
public Dog() {
super("dog");
}
}
public class Cat extends Pet {
public Cat() {
super("cat");
}
}
|
实现一种猫狗队列的结构, 要求如下:
- add, 将cat或dog类的实例放入队列中
- pollAll, 将队列中所有实例按照入队先后顺序出队
- pollDog, 将队列中dog类实例按入队顺序出队
- pollCat, 同上
- isEmpty, 检查队列中是否还有元素
- isDogEmpty, 检查队列中是否有dog类实例
- isCatEmpty, 检查队列中是否有cat类实例
思路
用三个队列, 一个cat队列只存放cat实例, 一个dog队列只存放dog实例, 再用总队列存放所有实例.
但是这样移除元素的时候, 总队列怎么更新? 比如队列顺序是 {cat1, dog1, dog2}, 调用pollDog(), 无法维护
加一层封装尝试解决问题, 用一个容器类PetQueueItem来封装Pet及其子类, 同时增加count属性来表示全局入队顺序
果然没有什么问题是加一层封装解决不了的QAQ
代码实现
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| public class DogCatQueue {
public class Pet {
private String type;
public Pet(String type) {
this.type = type;
}
public String getPetType() {
return this.type;
}
}
public class Dog extends Pet {
public Dog() {
super("dog");
}
}
public class Cat extends Pet {
public Cat() {
super("cat");
}
}
public class PetQueueItem {
private Pet pet;
private Long count;
public PetQueueItem(Pet pet, Long count) {
this.pet = pet;
this.count = count;
}
public Pet getPet() {
return this.pet;
}
public Long getCount() {
return this.count;
}
public String getPetType() {
return this.pet.getPetType();
}
}
private Queue<PetQueueItem> dogQueue;
private Queue<PetQueueItem> catQueue;
private Long count;
public DogCatQueue() {
this.dogQueue = new LinkedList<PetQueueItem>();
this.catQueue = new LinkedList<PetQueueItem>();
this.count = 0L;
}
public void add(Pet pet) {
if (pet.getPetType().equals("dog")) {
this.dogQueue.add(new PetQueueItem(pet, count++));
} else if (pet.getPetType().equals("cat")) {
this.catQueue.add(new PetQueueItem(pet, count++));
} else {
throw new RuntimeException("Pet must be dog or cat!");
}
}
public Pet pollAll() {
if (isDogEmpty() && isCatEmpty()) {
throw new RuntimeException("Your queue is empty!");
}
if (!isDogEmpty() && !isCatEmpty()) {
if (dogQueue.peek().getCount() < catQueue.peek().getCount()) {
return dogQueue.poll().getPet();
} else {
return catQueue.poll().getPet();
}
}
if (!isDogEmpty()) {
return dogQueue.poll().getPet();
}
return catQueue.poll().getPet();
}
public Dog pollDog() {
if (isDogEmpty()) {
throw new RuntimeException("Your dog queue is empty!");
}
return (Dog) dogQueue.poll().getPet();
}
public Cat pollCat() {
if (isCatEmpty()) {
throw new RuntimeException("Your cat queue is empty!");
}
return (Cat) dogQueue.poll().getPet();
}
public Boolean isEmpty() {
return isDogEmpty() && isCatEmpty();
}
public Boolean isDogEmpty() {
return dogQueue.isEmpty();
}
public Boolean isCatEmpty() {
return catQueue.isEmpty();
}
}
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