剑指offer：用两个栈实现队列

添加链接描述

class CQueue {
    stack<int> s1, s2;
public:
    CQueue() {
        while (!s1.empty())
        {
            s1.pop();
        }
        while (!s2.empty())
        {
            s2.pop();
        }
    }
    
    void appendTail(int value) {
        s1.push(value);
    }
    
    int deleteHead() {
        if (s2.empty())
        {
            while (!s1.empty())
            {
                int t = s1.top();
                s1.pop();
                s2.push(t);
            }
        }

        if (s2.empty()) return -1;
        else
        {
            int del = s2.top();
            s2.pop();
            return del;
        }
        
    }
};

/**
 * Your CQueue object will be instantiated and called as such:
 * CQueue* obj = new CQueue();
 * obj->appendTail(value);
 * int param_2 = obj->deleteHead();
 */