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  1. /* package whatever; // don't place package name! */
  2.  
  3. import java.util.*;
  4. import java.lang.*;
  5. import java.io.*;
  6.  
  7. /* Name of the class has to be "Main" only if the class is public. */
  8. class Ideone
  9. {
  10. 	public static void main (String[] args) throws java.lang.Exception
  11. 	{
  12. 		int[] hgram = new int[9];
  13. 		Random rng = new Random();
  14. 		for (int i = 0; i < 30000; i++) {
  15. 			int[] a = getRandomSelection( 2, 3, rng );
  16. 			hgram[3*a[0] + a[1]]++;
  17. 		}
  18. 		for (int i = 0; i < hgram.length; i++) {
  19. 			if (i > 0) System.out.print(", ");
  20. 			System.out.print(hgram[i]);
  21. 		}
  22. 	}
  23.  
  24. 	public static int[] getRandomSelection (int k, int n, Random rng) {
  25.     	if (k > n) throw new IllegalArgumentException(
  26.         	"Cannot choose " + k + " elements out of " + n + "."
  27.     	);
  28.  
  29. 	    HashMap<Integer, Integer> hash = new HashMap<Integer, Integer>(2 * k);
  30.     	int[] output = new int[k];
  31.  
  32. 		for (int i = 0; i < k; i++) {
  33.         	int j = i + rng.nextInt(n - i);
  34.             output[i] = (hash.containsKey(j) ? hash.remove(j) : j);
  35.             if (j > i) hash.put(j, hash.containsKey(i) ? hash.remove(i) : i);
  36.     	}
  37.     	return output;
  38. 	}
  39. }
Success #stdin #stdout 0.13s 320256KB
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stdin
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Standard input is empty
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0, 4954, 5017, 4976, 0, 4961, 4958, 5134, 0
https://ideone.com/kSAmbo
language:
Java (HotSpot 12)
created:
8 years ago
visibility:
public

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