leetcode栈之用两个栈实现队列

用两个栈实现一个队列。队列的声明如下，请实现它的两个函数 appendTail 和 deleteHead ，分别完成在队列尾部插入整数和在队列头部删除整数的功能。(若队列中没有元素，deleteHead 操作返回 -1 )示例 1：输入：["CQueue","appendTail","deleteHead","deleteHead"][[],[3],[],[]]输出：[null,null,3,-1]示例 2：输入：["CQueue","deleteHead","appendTail","appendTail","deleteHead","deleteHead"][[],[],[5],[2],[],[]]输出：[null,-1,null,null,5,2]提示：    1 <= values <= 10000    最多会对 appendTail、deleteHead 进行 10000 次调用来源：力扣（LeetCode）链接：https://leetcode-cn.com/problems/yong-liang-ge-zhan-shi-xian-dui-lie-lcof著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

class CQueue {    Stack<Integer> in;    Stack<Integer> out;    public CQueue() {        in = new Stack<>();        out = new Stack<>();    }    public void appendTail(int value) {        while(!out.isEmpty()){            in.push(out.pop());        }        in.push(value);    }    public int deleteHead() {        while(!in.isEmpty()){            out.push(in.pop());        }        if(out.isEmpty()){            return -1;        }        return out.pop();    }}/** * Your CQueue object will be instantiated and called as such: * CQueue obj = new CQueue(); * obj.appendTail(value); * int param_2 = obj.deleteHead(); */