MinStack2.java

import java.util.ArrayList;
import java.util.List;

/**
 * Created by yasin_000 on 22.8.2017.
 */
public class MinStack2 {
 List<Integer> records;
 List<Integer> mins;

 MinStack2(){
 records = new ArrayList<>();
 mins = new ArrayList<>();
 }

 public void push(int x){
 records.add(x);
 if (mins.isEmpty() || x <= mins.get(mins.size() - 1))
 mins.add(x);
 }

 public int pop(){
 if (records.isEmpty())
 throw new IllegalStateException("Stack is empty");
 int top = records.remove(size() - 1);
 if (!mins.isEmpty() && top == mins.get(mins.size() - 1))
 mins.remove(mins.size() - 1);
 return top;
 }

 public int peek(){
 if (records.isEmpty())
 throw new IllegalStateException("Stack is empty");
 return records.get(size() - 1) ;
 }

 public int getMin(){
 if (!records.isEmpty())
 return mins.get(mins.size() - 1);
 return -1;
 }

 public int size(){
 return records.size();
 }
}