155. Min Stack

class MinStack {
public:
    vector<pair<int,int>> st;        //we have make a vector
    MinStack() {
        
    }
    
    void push(int val) {
        if(st.empty()){
            pair<int,int>p;// = make_pair(val,val);
            p.first = val;
            p.second = val;
            st.push_back(p);
        }
        else{
            pair<int,int>p;
            p.first = val;
            p.second = min(val, st.back().second);
            st.push_back(p);
        }
    }
    
    void pop() {
        st.pop_back();
    }
    
    int top() {
        return st.back().first;
    }
    
    int getMin() {
        return st.back().second;
    }
};