leetcode 155. 最小栈(开启一个辅助栈 每次push min(辅助栈栈顶,x))

class MinStack {
public:
    stack<int>s;
    stack<int>ss;
    void push(int x) {s.push(x),ss.push(ss.empty()?x:min(x,ss.top()));}

    void pop() {s.pop(),ss.pop();}

    int top() {return s.top();}

    int getMin() {return ss.top();}
};