Mystery.java

import java.util.Comparator;
import java.util.List;

/**
  ???
**/
public class Mystery<T extends Comparable<? super T>> implements Comparator<List<T>> {

    @Override
    public int compare(List<T> l1, List<T> l2) {
        for (int i = 0; i < l1.size() && i < l2.size(); i++) {
            T c1 = l1.get(i);
            T c2 = l2.get(i);
            int c = c1.compareTo(c2);
            if (c != 0) {
                return c;
            }
        }
      
        return l2.size() - l1.size();
    }
}