155.cpp

#include <climits>
#include <stack>
using namespace std;

class MinStack {
public:
    stack<pair<int,int>> st;
    int minimum = INT_MAX;
    MinStack() {}
    
    void push(int val) {
        if (st.empty()) {
            st.push({val,val});
        } else {
            minimum = min(val, st.top().second);
            st.push({val, minimum});
        }
    }
    
    void pop() {
        st.pop(); 
    }
    
    int top() {
        return st.top().first; 
    }
    
    int getMin() {
        return st.top().second;
    }
};

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