两个栈实现链表

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

#include <iostream>
#include <stack>
using namespace std;

class CQueue {
public:
    CQueue() {

    }
    
    void appendTail(int value) {
        s1.push(value);
        return;
    }
    
    int deleteHead() {
        if (s2.empty()) {
            while (!s1.empty()) {
                s2.push(s1.top());
                s1.pop();
            }
        }
        if (s2.empty()) {
            return -1;
        } else {
            int tmp = s2.top();
            s2.pop();
            return tmp;
        }
    }
public:
    stack<int> s1;
    stack<int> s2;
};

int main()
{
    CQueue *test = new CQueue();
    test->appendTail(2);
    test->appendTail(3);
    test->appendTail(4);
    std::cout << test->deleteHead() << endl; // 2
    std::cout << test->deleteHead() << endl; // 3
    std::cout << test->deleteHead() << endl; // 4
    std::cout << test->deleteHead() << endl; // -1
    test->appendTail(4);
    test->appendTail(5);
    test->appendTail(6);
    std::cout << test->deleteHead() << endl; // 4
    test->appendTail(7);
    std::cout << test->deleteHead() << endl; // 5

    delete test;
    system("pause");
    return 0;
}