131工结

class MinStack {
//变量的初始化可以在private里写
private:
    stack<int> s;
    stack<int> min;
public:
    /** initialize your data structure here. */
    //初始化就是把其全部置空
    MinStack() {
        while(!s.empty())
        {
            s.pop();
        }
        while(!min.empty())
        {
            min.pop();
        }
    }
    
    void push(int x) {
        //如果没有判空，会错误，因为 无法直接比较top
        if(s.empty())
        {
            s.push(x);
            min.push(x);
        }
        else
        {
            s.push(x);
            if(x<=min.top())
            {
                min.push(x);
            }
            else
            {
                min.push(min.top());
            }
        }
    }
    
    void pop() {
        s.pop();
        min.pop();
    }
    
    int top() {
        return s.top();
        
    }
    
    int getMin() {
        return min.top();
    }
};

/**
 * Your MinStack object will be instantiated and called as such:
 * MinStack* obj = new MinStack();
 * obj->push(x);
 * obj->pop();
 * int param_3 = obj->top();
 * int param_4 = obj->getMin();
 */