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  1. import java.util.*;
  2. import java.lang.*;
  3. import java.io.*;
  4.  
  5. /* Name of the class has to be "Main" only if the class is public. */
  6. class Ideone
  7. {
  8. 	public static void main (String[] args) throws java.lang.Exception
  9. 	{
  10. 		String input = "this is a markov chain, this is not a markov chain";
  11. 		final int N = 2;
  12. 		HashMap<String, HashMap<String, Integer>> prefixes = generatePrefixes(input, N);
  13.  
  14.  
  15. 	}
  16.  
  17. 	public static HashMap<String, HashMap<String, Integer>> generatePrefixes(String input, int n)
  18. 	{
  19. 		HashMap<String, HashMap<String, Integer>> prefixes = new HashMap<String, HashMap<String, Integer>>();
  20. 		String[] words = input.split(" ");
  21. 		for (int i = 0; i < words.length-2; i++)
  22. 		{
  23. 			HashMap<String, Integer> suffixes = new HashMap<String, Integer>();
  24. 			suffixes.put(words[i+2], 1);
  25.  
  26. 			if (prefixes.get(words[i] + words[i+1]).get(words[i+2]) == null)
  27. 			{
  28. 				prefixes.put(words[i] + words[i+1], suffixes);
  29. 			}
  30. 			else
  31. 			{
  32. 				suffixes.put(words[i+2], prefixes.get(words[i] + words[i+1]).get(words[i+2])+1);
  33. 				prefixes.put(words[i] + words[i+1], suffixes);
  34. 			}
  35. 		}
  36. 		return prefixes;
  37. 	}
  38.  
  39.  
  40. }
Runtime error #stdin #stdout #stderr 0.09s 320512KB
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Standard input is empty
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Standard output is empty
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Exception in thread "main" java.lang.NullPointerException
	at Ideone.generatePrefixes(Main.java:26)
	at Ideone.main(Main.java:12)
https://ideone.com/T7VCw4
language:
Java (HotSpot 12)
created:
7 years ago
visibility:
public

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