自己实现数据结构系列四---Queue

一.代码部分

1.定义接口：

public interface Queue<E> {

    void enqueue(E e);
    E dequeue();
    E getFront();
    int getSize();
    boolean isEmpty();

}

2.基于数组的实现

public class ArrayQueue<E> implements Queue<E> {

    private ArrayList<E> arrayList;
    public ArrayQueue(int capacity){
        arrayList = new ArrayList<>(capacity);
    }
    public ArrayQueue(){
        arrayList = new ArrayList<>();
    }

    @Override
    public void enqueue(E e) {
        arrayList.addLast(e);
    }

    @Override
    public E dequeue() {
        return arrayList.removeFirst();
    }

    @Override
    public E getFront() {
        return arrayList.get(0);
    }

    @Override
    public int getSize() {
        return arrayList.getSize();
    }

    @Override
    public boolean isEmpty() {
        return arrayList.isEmpty();
    }

}

3.改进链表实现队列：

public class LinkedListQueue<E> implements Queue<E> {

    //节点,用来存放数据：数据+下一个元素的引用
    private class Node{
        private E e;
        private Node next;
        public Node(E e,Node next){
            this.e = e;
            this.next = next;
        }
        public Node(E e){
            this(e,null);
        }
        public Node(){
            this(null,null);
        }
        public String toString(){
            return e.toString();
        }
    }
    private Node head;//头节点
    private Node tail;//尾节点
    private int size;

    public LinkedListQueue(){
        head = null;
        tail = null;
        size =0;
    } 

    @Override
    public void enqueue(E e) {
        if (tail == null){
            tail = new Node(e);
            head = tail;
        }else {
            tail.next = new Node(e);
            tail = tail.next;
        }
        size++;
    }

    @Override
    public E dequeue() {
        if(isEmpty())
            throw new IllegalArgumentException("empty");
        Node retNode = head;
        head = head.next;
        retNode.next = null;

        if (head == null){
            tail = null;
        }
        size--;
        return retNode.e;
    }

    @Override
    public E getFront() {
        if(isEmpty())
            throw new IllegalArgumentException("empty");
        return head.e;
    }

    @Override
    public int getSize() {
        return size;
    }

    @Override
    public boolean isEmpty() {
        return size ==0;
    }

    @Override
    public String toString() {
        StringBuilder res = new StringBuilder();
        res.append("queue:front");
        Node cur = head;
        while (cur != null){
            res.append(cur + "->");
            cur = cur.next;

        }
        res.append("null tail");
        return res.toString();
    }
}

3.循环队列：

public class LoopQueue<E> {

    private E[] data;
    private int front;//队列头
    private int tail;//队列尾
    private int size;

    /**
     * 初始化容量的构造方法
     * @param capacity
     */
    public LoopQueue(int capacity){
        data = (E[]) new Object[capacity+1]; //注意加一
        front = 0;
        tail = 0;
        size = 0;
    }

    /**
     * 无参的构造方法
     */
    public LoopQueue(){
        this(10);
    }

    public int getCapacity(){
        return data.length-1;
    }

    public boolean isEmpty(){
        return front == tail;
    }

    public int getSize(){
        return size;
    }

    /**
     * 改变数组容量
     * @param newCapacity
     */
    private void resize(int newCapacity){
        E[] newData = (E[]) new Object[newCapacity+1];
        for (int i = 0; i < size; i++) {
            newData[i] = data[(i+front)%data.length];
        }
        data = newData;
        front = 0;
        tail = size;
    }

    /**
     * 入队
     * @param e
     */
    public void enqueue(E e){
        if ((tail+1)%data.length == front){
            resize(getCapacity()*2);
        }
        data[tail] = e;
        tail = (tail+1)%data.length;//注意这里不是tail++
        size++;
    }

    /**
     * 出队
     * @return
     */
    public E dequeue(){
        if (isEmpty()){
            throw new IllegalArgumentException("can't dequeue");
        }
        E ret = data[front];
        data[front] = null;
        front = (front+1)%data.length;//注意这里不是front++
        size--;
        if(size == getCapacity()/4 && getCapacity()/2 != 0){
            resize(getCapacity()/2);
        }
        return ret;
    }

    /**
     * 队列头
     * @return
     */
    public E getFront(){
        if (isEmpty()){
            throw new IllegalArgumentException("queue is empty");
        }
        return data[front];
    }

    @Override
    public String toString() {

        StringBuilder res = new StringBuilder();
        res.append(String.format("queue size =%d, capacity = %d\n"),size,getCapacity());
        res.append("front [");
        for (int i = front; i != tail; i = (i=1)%data.length) {
            res.append(data[i]);
            if((i+1)%data.length != tail){
                res.append(",");
            }
        }
        res.append("] tail");
        return res.toString();
    }
}