[JZ 用两个栈实现队列]

class CQueue {
    LinkedList<Integer> stack1,stack2;
    public CQueue() {
        stack1 = new LinkedList<Integer>();
        stack2 = new LinkedList<Integer>();
    }

    public void appendTail(int value) {
        stack1.add(value);
    }

    public int deleteHead() {
        if(stack2.isEmpty()){
            if (stack1.isEmpty()){
                return -1;
            }
            while (!stack1.isEmpty()){
                stack2.add(stack1.pop());
            }
            return stack2.pop();
        }
        return stack2.pop();
    }
}