基于数组的循环队列和基于链表的队列

数据的插入和取出涉及对当前数据量nItems属性的修改，大量的插入、移除操作时，对nItems属性的操作可能影响性能，可参考不包含数据项个数属性的队列实现。

基于数组的循环队列

包含数据项个数属性

package datastructure.c4.queue.queuedef;public class Queue {private int maxSize;private long[] queArray;private int front;private int rear;private int nItems;public Queue(int s){maxSize=s;queArray=new long[maxSize];front=0;rear=-1;nItems=0;}public void insert(long j){if(rear==maxSize-1){rear=-1;}queArray[++rear]=j;nItems++;}public long remove(){long temp=queArray[front++];if(front==maxSize){front=0;}nItems--;return temp;}public long peekFront(){return queArray[front];}public boolean isEmpty(){return (nItems==0);}public boolean isFull(){return (nItems==maxSize);}public int size(){return nItems;}}

package datastructure.c4.queue.queuedef;public class QueueApp {public static void main(String[] args) {Queue theQueue=new Queue(5);theQueue.insert(10);theQueue.insert(20);theQueue.insert(30);theQueue.insert(40);theQueue.remove();theQueue.remove();theQueue.remove();theQueue.insert(50);theQueue.insert(60);theQueue.insert(70);theQueue.insert(80);while(!theQueue.isEmpty()){long n = theQueue.remove();System.out.print(n);System.out.print("  ");}System.out.println("");}}

不包含数据项个数属性

package datastructure.c4.queue.nonitems;public class QueueWithoutN {private int maxSize;private long[] queArray;private int front;/** * rear作为写值的标志，插入时会在rear的下一个位置写入新值， * 当rear=maxSize-1，也就是rear指向的数组的最后一个值， * 要将rear设为-1，形成循环队列 */private int rear;public QueueWithoutN(int s){maxSize=s+1;queArray=new long[maxSize];front=0;rear=-1;}/** * 新值位于rear的后一个位置 * @param j */public void insert(long j){if(rear==maxSize-1){rear=-1;}queArray[++rear]=j;}/** * 取值时取front位置当前值，front后移一位 * 当front是数组最后一个元素时，后移一位后front=maxSize， * 令front=0 * @return */public long remove(){long temp=queArray[front++];if(front==maxSize){front=0;}return temp;}public long peek(){return queArray[front];}/** * 1、rear+1==front说明下次写入值会覆盖front当前值，说明队列为空 * 2、front+maxSize-1==rear --> rear-front=maxSize-1（数组下标最大值）， * 只能rear=maxSize-1，front=0（front是数组第一个元素，rear是数组最后一个元素）， * 下次写入也会覆盖front当前值 * @return front与rear位置差1的所有情况返回true */public boolean isEmpty(){return (rear+1==front || front+maxSize-1==rear);}/** * 队列为空时rear位于front前一个位置， * 写满时，rear位于front前两个位置 * @return front与rear位置差2的所有情况返回true */public boolean isFull(){return (rear+2==front || front+maxSize-2==rear);}/** * 1、rear>=front，说明未循环，元素数量为rear与front之间的元素数 * 2、rear<front，说明已循环插入，(maxSize-front)为front到数组最后的元素数， * (rear+1)为数组开始（下标为0）到rear间的元素数 * @return */public int size(){if(rear>=front){return rear-front+1;}else{return (maxSize-front)+(rear+1);}}}

基于双端链表的队列

package datastructure.c5.linklist.linkqueue;public class Link {public long dData;public Link next;public Link(long d){dData=d;}public void displayLink(){System.out.print(dData+"  ");}}

package datastructure.c5.linklist.linkqueue;public class FirstLastList {private Link first;private Link last;public FirstLastList(){first=null;last=null;}public boolean isEmpty(){return first==null;}public void insertLast(long dd){Link newLink =new Link(dd);if(isEmpty()){first=newLink;}else{last.next=newLink;}last=newLink;}public long deleteFirst(){long temp=first.dData;if(first.next==null){last=null;}first=first.next;return temp;}public void displayList(){Link current=first;while(current!=null){current.displayLink();current=current.next;}System.out.println("");}}

package datastructure.c5.linklist.linkqueue;public class LinkQueue {private FirstLastList theList;public LinkQueue(){theList=new FirstLastList();}public boolean isEmpty(){return theList.isEmpty();}public void insert(long j){theList.insertLast(j);}public long remove(){return theList.deleteFirst();}public void displayQueue(){System.out.print("Queue (front-->rear):");theList.displayList();}}

package datastructure.c5.linklist.linkqueue;public class LinkQueueApp {public static void main(String[] args) {LinkQueue theQueue=new LinkQueue();theQueue.insert(20);theQueue.insert(40);theQueue.displayQueue();theQueue.insert(60);theQueue.insert(80);theQueue.displayQueue();theQueue.remove();theQueue.remove();theQueue.displayQueue();}}