algorithm_1

## 使用2个队列实现栈 ##

class MyStack {

    Queue[] q = new LinkedBlockingQueue[2];
    // 记录非空队列的脚标
    int index = -1;

    public MyStack() {
        this.q[0] = new LinkedBlockingQueue();
        this.q[1] = new LinkedBlockingQueue();
    }

    public void push(Object element) {
        if (index == -1) {
            q[0].add(element);
            index = 0;
        } else {
            q[index].add(element);
        }
    }

    public Object pop() {
        if (index == -1) {
            System.out.println("Task is empty !");
            return null;

        } else {
            while (q[index].size() > 1) {
                q[1-index].add(q[index].poll());
            }
            Object item = q[index].poll();

            if (q[1- index].isEmpty()) {
                index = -1;
            } else {
                index = 1 - index;
            }
            return item;
        }
    }

    public int size() {
        return q[index].size();
    }

}


## 使用2个栈实现队列 ##

class MyQueue {

    Stack orderedStack = new Stack();
    Stack reverseStack = new Stack();

    public void add(Object element) {
        reverseStack.push(element);
    }

    public Object poll() {
        if (!orderedStack.isEmpty()) {
            return orderedStack.pop();

        } else {
            while (!reverseStack.isEmpty()) {
                orderedStack.push(reverseStack.pop());
            }

            if (orderedStack.isEmpty()) {
                System.out.println("Queue is empty !");
                return null;
            } else {
                return orderedStack.pop();
            }
        }
    }

    public int size() {
        return orderedStack.size() + reverseStack.size();
    }

}