动态数组-----双端队列的实现

双端队列定义

Deque接口

public interface Deque<E> extends Queue<E> {
    public void addFirst(E element);
    public void addLast(E element);
    public E removeFirst();
    public E removeLast();
    public E getFirst();
    public E getLast();
    public int size();
    public boolean isEmpty();
    public void clear();
}

ArrayDeque类

package shixianClass;

import shujujiegou_interface.Deque;
import shujujiegou_interface.Stack;

import java.util.Arrays;
import java.util.Iterator;

//双端队列  除了有自身的特点外，也可以当做队列和栈使用
//没有提供在任意角标处操作元素的功能
public class ArrayDeque<E> implements Deque<E>, Stack<E> {

    private E []data;
    private int front;//队首指针   front==rear 双端队列为空
    private int rear; //队尾指针   (rear+1)%data.length==front  双端队列为满
    private int size; //有效元素的个数
    private static int DEFAULT_SIZE=10;

    public ArrayDeque(){
        this(DEFAULT_SIZE);
    }
    public ArrayDeque(int capacity){
        data=(E[])new Object[capacity+1];
        front=0;
        rear=0;
        size=0;
    }

    //在Deque的队首添加一个元素
    @Override
    public void addFirst(E element) {
       //先判断Deque是否满的
        if(isExpansion()){
            resize(data.length*2-1);
        }
        front= (front-1+data.length)%data.length ;
        data[front]=element;
        size++;
    }

    private void resize(int newLength) {
        E[] newData=(E[])new Object[newLength];
        int index=0;
        for(int i=front;i!=rear;i=(i+1)%data.length){
            newData[index++]=data[i];
        }
        front=0;
        rear=index;
        data=newData;
    }

    private boolean isExpansion() {
        return (rear+1)%data.length==front;
    }

    //在Deque的队尾添加一个元素
    @Override
    public void addLast(E element) {
        //先判断Deque是否满的
        if(isExpansion()){
            resize(data.length*2-1);
        }
        data[rear]=element;
        rear=(rear+1)%data.length;
        size++;
    }

    //在Deque队首删除一个元素
    @Override
    public E removeFirst() {
        if(isEmpty()){
          throw new NullPointerException("Deque is null");
        }
        E ret =data[front];
        front=(front+1)%data.length;
        size--;
        //在判断是否需要缩容
        if(isShrink()){
            resize(data.length/2+1);
        }
        return ret;
    }

    private boolean isShrink() {
        return size==(data.length-1)/4&&data.length-1>DEFAULT_SIZE;
    }


    //在Deque队尾删除一个元素
    @Override
    public E removeLast() {
        if(isEmpty()){
            throw new NullPointerException("Deque is null");
        }
        rear=(rear-1+data.length)/data.length;
        E ret=data[rear];
        size--;
        //在判断是否需要缩容
        if(isShrink()){
            resize(data.length/2+1);
        }
        return ret;
    }

    //获取队首元素
    @Override
    public E getFirst() {
        return data[front];
    }

    //获取队尾元素
    @Override
    public E getLast() {
        return data[(rear-1+data.length)%data.length];
    }

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

    //判断是否为空
    @Override
    public boolean isEmpty() {
        return size==0&&front==rear;
    }

    //栈  入栈->addLast() front栈底 rear栈顶
    @Override
    public void push(E element) {
       addLast(element);
    }

    //栈 出栈->removeLast() front栈底 rear栈顶
    @Override
    public E pop() {
        return removeLast();
    }

    //栈 获取栈顶元素 ->getLast()  front栈底 rear栈顶
    @Override
    public E peek() {
        return getLast();
    }

    //队列 入队-> addLast() front队首  rear 队尾
    @Override
    public void offer(E element) {
     addLast(element);
    }

    //队列 入队-> removeFirst() front队首  rear 队尾
    @Override
    public E poll() {
        return removeLast();
    }

    //队列 获取队首元素-> getFirst() front队首  rear 队尾
    @Override
    public E element() {
        return getFirst();
    }

    @Override
    public void clear() {
         data=(E[])new Object[DEFAULT_SIZE+1];
         front=0;
         rear=0;
         size=0;
    }

    @Override
    public String toString() {
        StringBuilder sb=new StringBuilder(String.format("ArrayDeque:%d/%d[",size,data.length-1));
        if (isEmpty()){
            sb.append(']');
        }else {
            for (int i=front;i!=rear;i=(i+1)%data.length){
                sb.append(data[i]);
                if((i+1)%data.length==rear){
                    sb.append(']');
                }else {
                    sb.append(',');
                }
            }
        }
        return sb.toString();
    }

    @Override
    public Iterator<E> iterator() {
        return new ArrDequeIterator();
    }
    //默认的迭代方向是从front-rear
    class ArrDequeIterator implements Iterator<E>{
        private int cur=front;
        @Override
        public boolean hasNext() {
            return cur!=rear;
        }

        @Override
        public E next() {
            E ret=data[cur];
            cur=(cur+1)%data.length;
            return ret;
        }
    }
}

测试类

import shixianClass.ArrayDeque;

public class TestArrayDeque {
    public static void main(String[] args) {
        ArrayDeque<Integer> deque=new ArrayDeque<Integer>();
        System.out.println(deque);
        deque.addFirst(1);
        deque.addFirst(2);
        deque.addFirst(3);
        System.out.println(deque);
        deque.addLast(4);
        deque.addLast(5);
        deque.addLast(6);
        System.out.println(deque);
        System.out.println(deque.getFirst());
        System.out.println(deque.getLast());
        System.out.println(deque.removeFirst());
        System.out.println(deque.removeLast());
        System.out.println(deque);

        //Deque->stack
        for(int i=10;i<=15;i++){
            deque.push(i);
        }
        System.out.println(deque);
        System.out.println(deque.pop());
        System.out.println(deque);

        //Deque->Queue
        for(int i=100;i<=105;i++){
            deque.offer(i);
        }
        System.out.println(deque);
    }
}

最后

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