155. Min Stack (Leetcode)

class MinStack {
public:
    long Min;
    stack<long> s;
    MinStack() {
        Min = 1e16;
    }
    void push(int a) {
        if(s.empty()) {
            Min = 1e16;
            s.push(a);
        }
        else if(a >= Min)
        s.push(a);
        else 
        s.push(a - (Min - a));
        Min = min(Min, (long)a);
    }
    
    void pop() {
        long x = s.top();
        s.pop();
        if(x < Min) {
            Min = 2 * Min - x;
        }
    }
    
    int top() {
        long x = s.top();
        if(x < Min) {
            return (int)Min;
        }
        return (int)x;
    }
    
    int getMin() {
        return (int)Min;
    }
};