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
代码：
class CQueue {
Stack<Integer> stack1;
Stack<Integer> stack2;
public CQueue() {
stack1 = new Stack<Integer>();//添加栈
stack2 = new Stack<Integer>();
}
public void appendTail(int value) {
while(!stack2.isEmpty())
{
stack1.push(stack2.pop());
}
stack1.push(value);
}
public int deleteHead() {
while(!stack1.isEmpty())
{
stack2.push(stack1.pop());
}
if(stack2.isEmpty())
{
return -1;
}
return stack2.pop();
}
}
/**
* Your CQueue object will be instantiated and called as such:
* CQueue obj = new CQueue();
* obj.appendTail(value);
* int param_2 = obj.deleteHead();
*/
