剑指 Offer 09. 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）

 1 class CQueue {
 2     stack<int> stack1;
 3     stack<int> stack2;
 4 public:
 5     CQueue() {
 6 
 7     }
 8     
 9     void appendTail(int value) {
10         stack1.push(value);
11     }
12     
13     int deleteHead() {
14         if(stack1.empty()) return -1;
15        while(!stack1.empty())
16        {
17            int now=stack1.top();
18            stack1.pop();
19            stack2.push(now);
20        }
21        int res=stack2.top();
22        stack2.pop();
23         while(!stack2.empty())
24        {
25            int now=stack2.top();
26            stack1.push(now);
27            stack2.pop();       
28        }
29        return res;
30     }
31 };
32 
33 /**
34  * Your CQueue object will be instantiated and called as such:
35  * CQueue* obj = new CQueue();
36  * obj->appendTail(value);
37  * int param_2 = obj->deleteHead();
38  */