重温数据结构：队列的链式实现、顺序实现及循环队列

原创

ali莫川 2022-10-20 10:35:33 ©著作权

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1.队列的链式存储实现

队列接口：

package edu.njupt.zhb;
/*
 *@author: ZhengHaibo
 *2014-3-12  Nanjing,njupt,China
 */
public interface MyQueue {
  public void add(Object object);//从队列尾部加入一个元素
  public Object remove();//出列，返回队列头部的值，并将其删除
  public int getSize();//获取队列的大小
  public Object peek();//偷看队列的前端元素，但是不出列
  public boolean isEmpty();
}

链式存储的实现

/*
 * $filename: MyLinkedQueue.java,v $
 * $Date: 2014-3-12  $
 * Copyright (C) ZhengHaibo, Inc. All rights reserved.
 * This software is Made by Zhenghaibo.
 */
package edu.njupt.zhb;

import java.util.Queue;
import java.util.concurrent.LinkedBlockingQueue;

/*
 *@author: ZhengHaibo  

 *2014-3-12  Nanjing,njupt,China
 */
/**
 * 队列的链式实现
 */
public class MyLinkedQueue implements MyQueue{
  public class Node{
    Node next;
    Object data;
  }
  private Node front;//前面的指针
  private Node rear;//后面的指针
  private int size;
  public MyLinkedQueue(){
    front=new Node();
    front.next=null;
    rear=new Node();
    rear.next=null;
    size=0;
  }
  /**
   * 入列，从尾部添加元素
   */
  @Override
  public void add(Object object) {
    // TODO Auto-generated method stub
    Node node = new Node();
    node.data=object;
    if(size==0){//如果是空的
      front.next=node;
      rear.next=node;
      size++;
      return;
    }
    rear.next.next=node;//将尾节点指向新增节点
    rear.next=node;//将rear指针指向新增节点
    size++;
  }
  /**
   * 出列，从头部取出元素，并删除
   */
  @Override
  public Object remove() {
    // TODO Auto-generated method stub
    if(front.next!=null){
      Object object=front.next.data;//取出当前队列的头元素
      front.next=front.next.next;//删除第一个元素
      size--;
      return object;
    }
    return null;
  }
  @Override
  public int getSize() {
    // TODO Auto-generated method stub
    return size;
  }
  
  @Override
  public Object peek() {
    // TODO Auto-generated method stub
    return front.next.data;
  }
  @Override
  public boolean isEmpty() {
    // TODO Auto-generated method stub
    return size==0;
  }
  public static void main(String[] args) {
    MyQueue queue = new MyLinkedQueue();
    for(int i=0;i<20;i++){
      queue.add("str"+i);
    }
    while(!queue.isEmpty()){
      Object object=queue.remove();
      System.out.println((String)object);
    }
  }
}

队列的顺序存储：

/*
 * $filename: MyArrayQueue.java,v $
 * $Date: 2014-3-12  $
 * Copyright (C) ZhengHaibo, Inc. All rights reserved.
 * This software is Made by Zhenghaibo.
 */
package edu.njupt.zhb;
/*
 *@author: ZhengHaibo  
 *2014-3-12  Nanjing,njupt,China
 */
public class MyArrayQueue implements MyQueue {

  private int size;
  private int front;
  private int rear;
  final int INIT_LEN=10;//初始化长度
  final int INCREAMENT_LEN=10;//长度增量大小
  Object []objects;//用数组保存队列中的元素
  public MyArrayQueue(){
    size=0;
    front=0;
    rear=-1;
    objects = new Object[INIT_LEN];
  }
  @Override
  public void add(Object object) {
    // TODO Auto-generated method stub
    if(size+1==objects.length){//扩充数组
      Object []temp = new Object[objects.length+INCREAMENT_LEN];
      for(int i=0;i<objects.length;i++){
        temp[i]=objects[i];
      }
      objects=temp;
    }
    objects[++rear]=object;//将元素添加在队列的尾部
    size++;
  }

  @Override
  public Object remove() {
    // TODO Auto-generated method stub
    if(size==0){
      return null;
    }
    Object object = objects[front];//取出队列的头元素
    for(int i=0;i<objects.length-1;i++){//通过平移，删除已取出的元素
      objects[i]=objects[i+1];
    }
    size--;
    return object;
  }

  @Override
  public int getSize() {
    // TODO Auto-generated method stub
    return size;
  }

  @Override
  public Object peek() {
    // TODO Auto-generated method stub
    if(size==0){
      return null;
    }
    Object object = objects[front];//取出队列的头元素
    return object;
  }
  
  @Override
  public boolean isEmpty() {
    // TODO Auto-generated method stub
    return size==0;
  }
  public static void main(String[] args) {
    MyQueue queue = new MyArrayQueue();
    for(int i=0;i<20;i++){
      queue.add("str"+i);
    }
    while(!queue.isEmpty()){
      Object object=queue.remove();
      System.out.println((String)object);
    }
  }
}

循环队列：

原因：主要是解决队列的“假溢出”问题。其实上面的顺序实现方式已经有效避免了假溢出（通过平移的方式）。下面来看一下循环队列吧。

/*
 * $filename: MyArrayCircularQueue.java,v $
 * $Date: 2014-3-12  $
 * Copyright (C) ZhengHaibo, Inc. All rights reserved.
 * This software is Made by Zhenghaibo.
 */
package edu.njupt.zhb;
/*
 *@author: ZhengHaibo  
 *2014-3-12  Nanjing,njupt,China
 */
/**
 *实现循环队列操作：
 (1)为使入队和出队实现循环，可以利用取余运算符%
 (2)队头指针进一：front=(front+1) % maxSize
 (3)队尾指针进一：rear=(rear+1) % maxSize
 (4)空队列：当front==rear 时为空队列
 (5)满队列：当(rear+1) % maxSize ==front时为满队列。满队列时实际仍有一个元素的空间未使用。
 */
public class MyArrayCircularQueue implements MyQueue {

  private int front;
  private int rear;
  private final int maxSize = 10;
  private Object []objects;
  private int size;
  public MyArrayCircularQueue(){
    front=rear=0;
    size=0;
    objects=new Object[maxSize];
  }
  @Override
  public void add(Object object) {
    // TODO Auto-generated method stub
    if((rear+1)%maxSize==front){
      System.out.println("队列已满...");
      return;
    }
    rear=(rear+1)%maxSize;
    objects[rear]=object;
    size++;
  }

  @Override
  public Object remove() {
    // TODO Auto-generated method stub
    if(front==rear){
      System.out.println("队列已经空了...");
      return null;
    }
    front=(front+1)%maxSize;
    Object object = objects[front];
    size--;
    return object;
  }

  @Override
  public int getSize() {
    // TODO Auto-generated method stub
    return size;
  }

  @Override
  public Object peek() {
    // TODO Auto-generated method stub
    return objects[front+1];
  }

  @Override
  public boolean isEmpty() {
    // TODO Auto-generated method stub
    return front==rear;
  }
  
  public static void main(String[] args) {
    MyQueue queue = new MyArrayCircularQueue();
    for(int i=0;i<50;i++){
      queue.add("str"+i);
    }
    while(!queue.isEmpty()){
      Object object=queue.remove();
      System.out.println((String)object);
    }
  }
}