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  1. /* package whatever; // don't place package name! */
  2. import java.util.Arrays;
  3. import java.util.Iterator;
  4. import java.util.NoSuchElementException;
  5.  
  6.  
  7.  
  8. @SuppressWarnings("javadoc")
  9. class Combinations implements Iterable<int[]> {
  10.  
  11.     private class Yielder implements Iterator<int[]> {
  12.         private final long size;
  13.         private final long limit;
  14.         private long next = 0;
  15.         private final int[] stash; 
  16.  
  17.         public Yielder(int size) {
  18.             super();
  19.             this.size = size;
  20.             this.limit = 1 << size;
  21.             this.stash = new int[size];
  22.         }
  23.         @Override
  24.         public boolean hasNext() {
  25.             return next < limit;
  26.         }
  27.         @Override
  28.         public int[] next() {
  29.             if (next >= limit) {
  30.                 throw new NoSuchElementException();
  31.             }
  32.             int count = 0;
  33.             for (int b = 0; b < size; b++) {
  34.                 if ((next & (1 << b)) != 0) {
  35.                     stash[count++] = b;
  36.                 }
  37.             }
  38.             next++;
  39.             return Arrays.copyOf(stash, count);
  40.         }
  41.         @Override
  42.         public void remove() {
  43.             throw new UnsupportedOperationException();
  44.         }
  45.  
  46.     }
  47.  
  48.     private final int datasize;
  49.  
  50.     /**
  51.      * @param datasize
  52.      */
  53.     public Combinations(int datasize) {
  54.         super();
  55.         this.datasize = datasize;
  56.     }
  57.  
  58.     @Override
  59.     public Iterator<int[]> iterator() {
  60.         return new Yielder(datasize);
  61.     }
  62.  
  63.  
  64.  
  65.     public static void main(String[] args) {
  66.  
  67.         int cnt = 0;
  68.         for (int[] combination : new Combinations(3)) {
  69.             System.out.printf("Combination %6d size %2d members %s.%n", cnt++, combination.length, Arrays.toString(combination));
  70.         }
  71.  
  72.     }
  73. }
  74.  
Success #stdin #stdout 0.08s 380160KB
comments (?)
stdin 
Standard input is empty
stdout 
Combination      0 size  0 members [].
Combination      1 size  1 members [0].
Combination      2 size  1 members [1].
Combination      3 size  2 members [0, 1].
Combination      4 size  1 members [2].
Combination      5 size  2 members [0, 2].
Combination      6 size  2 members [1, 2].
Combination      7 size  3 members [0, 1, 2].
https://ideone.com/ZoS8QK
language:
Java (12.0.1)
created:
9 years ago
visibility:
public

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