数据结构 队列以及Java代码实现

1. 队列

队列是一种特殊的线性表，它只允许在表的前端（front）进行删除操作，而在表的后端（rear）进行插入操作。进行插入操作的端称为队尾，进行删除操作的端称为队头。队列中没有元素时，称为空队列。

• 队尾(rear)——允许插入的一端
• 队头(front)——允许删除的一端

队列特点：先进先出(FIFO)

结构模型：

2.顺序循环队列

/** * Queue * 队列的基本操作 * （1）清空队列 * （2）判断是否为空 * （3）元素的个数 * （4）入队列 * （5）出队列 * （6）取对头元素 * Created by heqianqian on 2017/7/14. */public interface Queue<T> {    /**     * 判断是否为空     */    boolean isEmpty();    /**     * 入队列     */    void enQueue(T obj);    /**     * 出队列     */    T deQueue();    /**     * 取队头元素     */    T peek();    /**     * 元素的个数     */    int size();    /**     * 清空队列     */    void clear();}

/** * ArrayQueue * 顺序循环队列 * Created by heqianqian on 2017/7/14. */public class ArrayQueue<T> implements Queue<T> {    private static final int DEFAULT_SIZE = 10;    private T[] queue;    private int front, rear;    private int size;    @SuppressWarnings("unchecked")    public ArrayQueue() {        front = rear = size = 0;        queue = (T[]) new Object[DEFAULT_SIZE];    }    @Override    public boolean isEmpty() {        return size == 0;    }    @Override    public void enQueue(T obj) {        if ((rear == front) && (size > 0)) {//队列已满            expand();        }        //队尾插入元素        queue[rear] = obj;        rear = (rear + 1) % DEFAULT_SIZE;        size++;    }    /**     * 扩容     */    @SuppressWarnings("unchecked")    private void expand() {        T[] arr = (T[]) new Object[DEFAULT_SIZE * 2];        System.arraycopy(queue, 0, arr, 0, size);    }    @Override    public T deQueue() {        if ((rear == front) && (size == 0)) {//队列为空            return null;        }        //队头取元素        T result = queue[front];        front = (front + 1) % DEFAULT_SIZE;        size--;        return result;    }    @Override    public T peek() {        return queue[front];    }    @Override    public int size() {        return size;    }    @Override    public void clear() {        front = rear = size = 0;    }    @Override    public String toString() {        StringBuilder sb = new StringBuilder();        sb.append("[");        for (int i = 0; i < size - 1; i++) {            sb.append(queue[i]).append(",");        }        sb.append(queue[size - 1]).append("]");        return sb.toString();    }}

3.链式队列

/** * Node * 链式队列的节点 * Created by heqianqian on 2017/7/14. */public class Node<T> {    public Node next;    public T data;    public Node(T data) {        this.data = data;        next = null;    }    @Override    public String toString() {        return data.toString();    }}

/** * LinkedQueue * 链式循环队列 * Created by heqianqian on 2017/7/14. */public class LinkedQueue<T> implements Queue<T> {    private Node<T> front, rear;    private int size;    @SuppressWarnings("unchecked")    public LinkedQueue() {        front = rear = new Node(null);        size = 0;    }    @Override    public boolean isEmpty() {        return size == 0;    }    @Override    public void enQueue(T obj) {        Node<T> node = new Node<T>(obj);        //队尾插入        rear.next = node;        rear = node;        size++;    }    @Override    @SuppressWarnings("unchecked")    public T deQueue() {        //队头出队        if (size <= 0) {            return null;        }        T data = (T) front.next.data;        front = front.next;        size--;        return data;    }    @Override    public T peek() {        return (T) front.next.data;    }    @Override    public int size() {        return size;    }    @Override    public void clear() {        size = 0;        front = rear;    }    @Override    public String toString() {        StringBuilder sb = new StringBuilder();        sb.append("[");        Node<T> temp = front.next;        while (temp != rear) {            sb.append(temp.data.toString()).append(",");            temp = temp.next;        }        sb.append(temp.data).append("]");        return sb.toString();    }}