剑指 Offer 09. 用两个栈实现队列C++

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]

class CQueue {
public:
    stack<int>stack1;
    stack<int>stack2;
    CQueue() {
    }
    
    void appendTail(int value) {
        stack1.push(value);
    }
    
    int deleteHead() {
     if(stack1.empty())  return -1;
     while(!stack1.empty()){
         stack2.push(stack1.top());
         stack1.pop();
     }
     int res = stack2.top();
     stack2.pop();
     while(!stack2.empty()){
         stack1.push(stack2.top());
         stack2.pop();
     }
     return res;

    }
};