OJ Board

I tried to understand problem 12071, but didn't understand what he problem asked to do actually, could anyone give a hint about what to solve here?
http://uva.onlinejudge.org/index.php?op ... oblem=3223

Getting Runtime Error, don't have a clue, help is appreciated
Also suggestion on how to improve the all substring generator code part is appreciated.


import java.util.ArrayList;
import java.util.HashSet;
import java.util.Scanner;
import java.io.BufferedReader;
import java.io.IOException;
import ...