MyArrayDeque

Queue接口

• ArrayDeque -》栈
• add(E)/offer(E)
• remove()/poll()
• elemtent()/peek()
  
  

Deque接口   双端队列

• Queue    Deque
• add(E)    addLast(E)
• offer(E)    offerLast(E)
• remove()    removeFirst()
• poll()  pollFirst()
• element()  getFirst()
• peek()  peekFirst()

Stack    Deque

• push(E)    addFirst(E)
• 无   offerFirst(E)
• pop()    removeFirst()
• 无   pollFirst()
• peek()   peekFirst()
• 无   getFirst()

class MyArrayDeque<E>{
    private E[] elements;
    private int head; //永远指向循环数组的头
    private int tail;//永远指向循环数组的尾
    private static int maxSize = 5;

    public MyArrayDeque(){
        this(5);
    }

    public MyArrayDeque(int capacity){
        elements = (E[])new Object[capacity];
        maxSize = capacity;
    }

    public void add(E value){
        //默认队尾添加
        //判满
        if((tail+1) % maxSize == head){
            //扩容
            elements = Arrays.copyOf(elements, 2*maxSize);
            maxSize = elements.length;
        }
        elements[tail] = value;
        tail = (tail+1) % maxSize;
    }

    public E remove(){
        //默认队头删除
        if(head == tail){
            throw new UnsupportedOperationException("the queue has been empty");
        }
        System.out.println(head);
        E result = elements[head];
        elements[head] = null; //方便垃圾回收
        head = (head +1 )% maxSize;
        return result;
    }

    public E get(){
        return elements[head];
    }

    public String toString(){
        StringBuilder strs = new StringBuilder();
        for(int i=head; i != tail+1; i=(i+1)%maxSize){
            strs.append(elements[i] + " ");
        }
        return strs.toString();
    }
}