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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.         String[] data = {"a", "b", "c", "d"};
  68.         int cnt = 0;
  69.         StringBuilder sb = new StringBuilder();
  70.         for (int[] combination : new Combinations(data.length)) {
  71.         	sb.setLength(0);
  72.         	for (int index : combination) {
  73.         		sb.append(data[index]);
  74.         	}
  75.             System.out.printf("Combination %6d size %2d members %15s %8s .%n", cnt++, combination.length, Arrays.toString(combination), sb.toString());
  76.         }
  77.  
  78.     }
  79. }
  80.  
Success #stdin #stdout 0.08s 380224KB
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Standard input is empty
stdout
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Combination      0 size  0 members              []          .
Combination      1 size  1 members             [0]        a .
Combination      2 size  1 members             [1]        b .
Combination      3 size  2 members          [0, 1]       ab .
Combination      4 size  1 members             [2]        c .
Combination      5 size  2 members          [0, 2]       ac .
Combination      6 size  2 members          [1, 2]       bc .
Combination      7 size  3 members       [0, 1, 2]      abc .
Combination      8 size  1 members             [3]        d .
Combination      9 size  2 members          [0, 3]       ad .
Combination     10 size  2 members          [1, 3]       bd .
Combination     11 size  3 members       [0, 1, 3]      abd .
Combination     12 size  2 members          [2, 3]       cd .
Combination     13 size  3 members       [0, 2, 3]      acd .
Combination     14 size  3 members       [1, 2, 3]      bcd .
Combination     15 size  4 members    [0, 1, 2, 3]     abcd .
https://ideone.com/UhJPZn
language:
Java (12.0.1)
created:
9 years ago
visibility:
public

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