java数据结构-08队列

public class Queue {
    private Stack<Integer> inStack;
    private Stack<Integer> outStack;

    public Queue() {
        inStack = new Stack<>();
        outStack = new Stack<>();
    }
    
    /** 入队 */
    public void push(int x) {
        inStack.push(x);
    }
    
    /** 出队 */
    public int pop() {
        checkOutStack();
        return outStack.pop();
    }
    
    /** 获取队头元素 */
    public int peek() {
        checkOutStack();
        return outStack.peek();
    }
    
    /** 是否为空 */
    public boolean empty() {
        return inStack.isEmpty() && outStack.isEmpty();
    }
    
    private void checkOutStack() {
        if (outStack.isEmpty()) {
            while (!inStack.isEmpty()) {
                outStack.push(inStack.pop());
            }
        }
    }
}

public class Queue<E> {
    private List<E> list = new LinkedList<>();//自己实现的类与接口，详细看单链表（一）
    
    public int size() {
        return list.size();
    }

    public boolean isEmpty() {
        return list.isEmpty();
    }
    
    public void clear() {
        list.clear();
    }

    public void enQueue(E element) {
        list.add(element);
    }

    public E deQueue() {
        return list.remove(0);
    }

    public E front() {
        return list.get(0);
    }
}