本題來自左神《程序員面試代碼指南》“貓狗隊列”題目。

題目

寵物、狗和貓的類如下：

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");}} }

實現(xiàn)一種貓狗隊列的結(jié)構(gòu)，要求如下：

• 用戶可以調(diào)用add() ，cat類或dog類的實例放入隊列中
• 用戶可以調(diào)用pollAll()，將隊列中所有實例按照隊列先后順序依次彈出
• 用戶可以調(diào)用pollDog()、pollCat()，將隊列中dog類、cat類的實例按照進(jìn)隊列的先后順序依次彈出
• 用戶可以調(diào)用isEmpty()，檢查隊列中是否還有dog、cat的實例
• 用戶可以調(diào)用isDogEmpty()、isCatEmpty()，分別檢查隊列中是否還有dog、cat的實例

解答

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();} }

package chapter_1_stackandqueue;import java.util.LinkedList; import java.util.Queue;public class Problem_04_DogCatQueue {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();} elsethrow 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();}}public static void main(String[] args) {DogCatQueue test = new DogCatQueue();Pet dog1 = new Dog();Pet cat1 = new Cat();Pet dog2 = new Dog();Pet cat2 = new Cat();Pet dog3 = new Dog();Pet cat3 = new Cat();test.add(dog1);test.add(cat1);test.add(dog2);test.add(cat2);test.add(dog3);test.add(cat3);test.add(dog1);test.add(cat1);test.add(dog2);test.add(cat2);test.add(dog3);test.add(cat3);test.add(dog1);test.add(cat1);test.add(dog2);test.add(cat2);test.add(dog3);test.add(cat3);while (!test.isDogQueueEmpty()) {System.out.println(test.pollDog().getPetType());}while (!test.isEmpty()) {System.out.println(test.pollAll().getPetType());}}}

運行結(jié)果：

dog dog dog dog dog dog dog dog dog cat cat cat cat cat cat cat cat cat 超強干貨來襲 云風(fēng)專訪：近40年碼齡，通宵達(dá)旦的技術(shù)人生

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