Min Max Stack Construction

• Time : O(1)
• Space : O(n)

using namespace std;

// Feel free to add new properties and methods to the class.
class MinMaxStack {
	vector<int> st;
	vector<int> mi, ma;
public:
  int peek() {
    if(!st.empty()) return st.back();
    return -1;
  }

  int pop() {
		if(st.empty()) return -1;
    int res = st.back();
		st.pop_back();
		if(mi.back() == st.size())
			mi.pop_back();
		if(ma.back() == st.size())
			ma.pop_back();
		
    return res;
  }

  void push(int number) {
    st.push_back(number);
		if(mi.empty() or st[mi.back()] > st.back()) {
			mi.push_back(st.size() - 1);
		}
		
		if(ma.empty() or st[ma.back()] < st.back()) {
			ma.push_back(st.size() - 1);
		}
  }

  int getMin() {
    if(st.empty()) return -1;
		return st[mi.back()];
  }

  int getMax() {
    if(st.empty()) return -1;
		return st[ma.back()];
  }
};