队列

抽象数据类型描述：

package org.zp.datastruct;public interface Queue {// 先进先出只能从队首删除、队尾插入public void clear();public void enqueue(Object obj);// 在队尾插入一个新元素public Object dequeue();// 删除并返回队首元素public boolean isEmpty();public int size();public Object peek();// 返回队首元素}

数组实现队列：

package org.zp.datastruct;public class ArrayQueue implements Queue {private static final int DEFAULT_SIZE = 10;private Object[] array;private int front;// 指向队首元素private int rear;// 指向队尾元素的后继位置private int count;// 构造方法，构造队列、初始化public ArrayQueue() {array = new Object[DEFAULT_SIZE];front = rear = count = 0;}public void clear() {for (int i = 0; i < array.length; i++) {array[i] = null;front = rear = count = 0;}}public Object dequeue() {if (count == 0) {throw new IllegalStateException();}Object obj = array[front];array[front++] = null;// 队首指针递增if (front == array.length) {front = 0;}count--;return obj;}/*  * 因为front=0时队列不一定为空，rear = array.length时队列不一定放满了。例如当rear =  * array.length时，front=3，(array[0]、、array[1]、array[2]这3个元素已经删除 * front才会移动到3) *  *  * */public void enqueue(Object obj) {if (count == array.length) {expand();}array[rear++] = obj;// 队尾指针递增if (rear == array.length) {rear = 0;}count++;}/* * 不论经过多少次的增加、删除，front与rear的具体位置在 哪里，最后当循环数组(队列) * 放满的时候：front = rear ，front + i其实就是将循环队列“拉直”，然后我们再给 * front赋值0，rear赋值array.length。当我们把数组元素复制到新数组之后队首位置就 * 在 新数组的左端啦。 *   */private void expand() {Object[] newArray = new Object[2 * array.length];for (int i = 0; i < count; i++) {newArray[i] = array[(front + i) % array.length];}front = 0;rear = array.length;array = newArray;}public boolean isEmpty() {return count == 0;}public Object peek() {if (count ==0) {throw new IllegalStateException();}return array[front];}public int size() {return count;}// 总是从头开始public String toString() {String buf = new String("[ ");for (int i = 0; i < count; i++) {if (i > 0) {buf += ", ";}buf += array[(front + i) % array.length].toString();}buf += " ]";return buf;}}

单向链表实现队列：

package org.zp.datastruct;public class LinkedQueue implements Queue {// 链表节点类private static class SLLNode {private Object data;private SLLNode next;public SLLNode() {}public SLLNode(Object data) {this.data = data;}public SLLNode(Object data, SLLNode next) {this.data = data;this.next = next;}public Object getData() {return data;}public void setData(Object data) {this.data = data;}public SLLNode getNext() {return next;}public void setNext(SLLNode next) {this.next = next;}public String toString() {return data.toString();}}private SLLNode front;// 指向单向链表第一个节点的引用private SLLNode rear;// 指向单向链表最后一个节点的引用private int count;public LinkedQueue () {clear();}public void clear() {front = rear = null;count = 0;}public Object dequeue() {if (count == 0) {throw new IllegalStateException();}Object obj = front.data;front = front.next;// 当前front没有了后继元素(即队列只剩下一个元素)，删除后链表为空，队列为空if (front == null) {rear = null;}count --;return obj;}public void enqueue(Object obj) {SLLNode temp = new SLLNode(obj, null);if (this.isEmpty()) {//队列为空front = temp;} else {rear.next = temp;}rear = temp;count ++;}public boolean isEmpty() {return count == 0;// return rear == null;}public Object peek() {if (this.isEmpty()) {throw new IllegalStateException();}return front.data;}public int size() {return count;}public String toString() {String buf = new String("[ ");for (SLLNode curr = front; curr != null; curr = curr.next) {if (curr != front) {buf += ", ";}buf += curr.data.toString();}buf += " ]";return buf;}}

测试类：

package org.zp.datastruct;public class QueueTest {/** * @param args */public static void main(String[] args) {Queue qa = new ArrayQueue();int[] array = new int[]{1,2,3,4,5,6,7,8,9};qa.enqueue("a");qa.enqueue(1);qa.enqueue(array);qa.enqueue(array[3]);qa.enqueue(array.length);qa.enqueue("6");System.out.println(qa.toString());qa.dequeue();//qa.dequeue();System.out.println(qa.toString());System.out.println(qa.size());Queue ql = new LinkedQueue();ql.enqueue(array);ql.enqueue(array.length);ql.enqueue(array.hashCode());System.out.println(ql.toString());}}

结果：

[ a, 1, [I@1fb8ee3, 4, 9, 6 ][ 1, [I@1fb8ee3, 4, 9, 6 ]5[ [I@1fb8ee3, 9, 33263331 ]