Class CombinationGenerator<T>
java.lang.Object
org.uncommons.maths.combinatorics.CombinationGenerator<T>
- Type Parameters:
T
- The type of element that the combinations are made from.
Combination generator for generating all combinations of a given size from
the specified set of elements. For performance reasons, this implementation
is restricted to operating with set sizes and combination lengths that produce
no more than 2^63 different combinations.
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Field Summary
Fields -
Constructor Summary
ConstructorsConstructorDescriptionCombinationGenerator
(Collection<T> elements, int combinationLength) Create a combination generator that generates all combinations of a specified length from the given set.CombinationGenerator
(T[] elements, int combinationLength) Create a combination generator that generates all combinations of a specified length from the given set. -
Method Summary
Modifier and TypeMethodDescriptionprivate void
Generate the indices into the elements array for the next combination.long
long
boolean
hasMore()
Are there more combinations?iterator()
Provides a read-only iterator for iterating over the combinations generated by this object.T[]
Generate the next combination and return an array containing the appropriate elements.T[]
nextCombinationAsArray
(T[] destination) Generate the next combination and return an array containing the appropriate elements.Generate the next combination and return a list containing the appropriate elements.nextCombinationAsList
(List<T> destination) Generate the next combination and return a list containing the appropriate elements.final void
reset()
Reset the combination generator.Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
Methods inherited from interface java.lang.Iterable
forEach, spliterator
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Field Details
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elements
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combinationIndices
private final int[] combinationIndices -
remainingCombinations
private long remainingCombinations -
totalCombinations
private long totalCombinations
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Constructor Details
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CombinationGenerator
Create a combination generator that generates all combinations of a specified length from the given set.- Parameters:
elements
- The set from which to generate combinations.combinationLength
- The length of the combinations to be generated.
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CombinationGenerator
Create a combination generator that generates all combinations of a specified length from the given set.- Parameters:
elements
- The set from which to generate combinations.combinationLength
- The length of the combinations to be generated.
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Method Details
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reset
public final void reset()Reset the combination generator. -
getRemainingCombinations
public long getRemainingCombinations()- Returns:
- The number of combinations not yet generated.
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hasMore
public boolean hasMore()Are there more combinations?- Returns:
- true if there are more combinations available, false otherwise.
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getTotalCombinations
public long getTotalCombinations()- Returns:
- The total number of combinations.
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nextCombinationAsArray
Generate the next combination and return an array containing the appropriate elements.- Returns:
- An array containing the elements that make up the next combination.
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nextCombinationAsArray
Generate the next combination and return an array containing the appropriate elements. This overloaded method allows the caller to provide an array that will be used and returned. The purpose of this is to improve performance when iterating over combinations. If thenextCombinationAsArray()
method is used it will create a new array every time. When iterating over combinations this will result in lots of short-lived objects that have to be garbage collected. This method allows a single array instance to be reused in such circumstances.- Parameters:
destination
- Provides an array to use to create the combination. The specified array must be the same length as a combination.- Returns:
- The provided array now containing the elements of the combination.
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nextCombinationAsList
Generate the next combination and return a list containing the appropriate elements.- Returns:
- A list containing the elements that make up the next combination.
- See Also:
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nextCombinationAsList
Generate the next combination and return a list containing the appropriate elements. This overloaded method allows the caller to provide a list that will be used and returned. The purpose of this is to improve performance when iterating over combinations. If thenextCombinationAsList()
method is used it will create a new list every time. When iterating over combinations this will result in lots of short-lived objects that have to be garbage collected. This method allows a single list instance to be reused in such circumstances.- Parameters:
destination
- Provides a list to use to create the combination.- Returns:
- The provided list now containing the elements of the combination.
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generateNextCombinationIndices
private void generateNextCombinationIndices()Generate the indices into the elements array for the next combination. The algorithm is from Kenneth H. Rosen, Discrete Mathematics and Its Applications, 2nd edition (NY: McGraw-Hill, 1991), p. 286. -
iterator
Provides a read-only iterator for iterating over the combinations generated by this object. This method is the implementation of the
Iterable
interface that permits instances of this class to be used with the new-style for loop.For example:
List<Integer> elements = Arrays.asList(1, 2, 3); CombinationGenerator<Integer> combinations = new CombinationGenerator(elements, 2); for (List<Integer> c : combinations) { // Do something with each combination. }
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