【打卡】牛客网：BM43 包含min函数的栈

模板的：

class Solution {
public:
    stack s1;
    stack s2;
    void push(int value) {
        s1.push(value);
        if(s2.empty() || s2.top() > value)
            s2.push(value);
        else
            s2.push(s2.top());
    }
    void pop() {
        s1.pop();
        s2.pop();
    }
    int top() {
        return s1.top();
    }
    int min() {
        return s2.top();
    }
};