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Very simple java library to generate permutations, combinations and other combinatorial sequences.

There is a newer version: 2.3





This package contains the subsets generators.


  A set A is a subset of a set B if A is "contained" inside B. A and B may
  coincide. The relationship of one set being a subset of another is called
  inclusion or sometimes containment.

  Examples:

  The set (1, 2) is a proper subset of (1, 2, 3).
  
Any set is a subset of itself, but not a proper subset.
  
The empty set, denoted by (), is also a subset of any given set X.


  All subsets of (1, 2, 3) are:

  ()
  
(1)
  
(2)
  
(1, 2)
  
(3)
  
(1, 3)
  
(2, 3)
  
(1, 2, 3)


  And code which generates all subsets of (one, two, three)


// Create an initial vector/set
ICombinatoricsVector<String> initialSet = CombinatoricsFactory.createVector(new String[] {
		"one", "two", "three" });

// Create an instance of the subset generator
Generator<String> gen = CombinatoricsFactory.createSubSetGenerator(initialSet);

// Print the subsets
for (ICombinatoricsVector<String> subSet : gen) {
	System.out.println(subSet);
}




  And the result of all 8 possible subsets



 CombinatoricsVector=([], size=0)
 CombinatoricsVector=([one], size=1)
 CombinatoricsVector=([two], size=1)
 CombinatoricsVector=([one, two], size=2)
 CombinatoricsVector=([three], size=1)
 CombinatoricsVector=([one, three], size=2)
 CombinatoricsVector=([two, three], size=2)
 CombinatoricsVector=([one, two, three], size=3)




  Version 2.0 of the combinatoricslib supports sets with duplicates. For
  example, if the original vector contains duplicates like (a, b, a, c), then
  the result will contain 14 subsets (instead of 16):


()
(a)
(b)
(a, b)
(a, a)
(b, a)
(a, b, a)
(c)
(a, c)
(b, c)
(a, b, c)
(a, a, c)
(b, a, c)
(a, b, a, c)



  If you still would like to treat the set with duplicates as not identical,
  you should create a generator and set the second parameter of the method
  CombinatoricsFactory.createSubSetGenerator() as false. In this
  case all 16 subsets will be generated.

  Note. If the initial vector contains duplicates then the method
  getNumberOfGeneratedObjects won't be able to return the number
  of the sub sets/lists. It will throw a runtime exception