de.caff.generics.util.combi

Class Combinations<T>

java.lang.Object

de.caff.generics.util.combi.Combinations<T>

Type Parameters:

T - element type of the incoming set

All Implemented Interfaces:

java.lang.Iterable<Indexable<T>>

public class Combinations<T>
extends java.lang.Object
implements java.lang.Iterable<Indexable<T>>

Create all combinations. This class takes care of creating all combination of n choose k lazily from a given set of objects.

Combinations returned will be ordered when considering the index into the incoming elements:

• Each single combination will appear in the order of the incoming elements. i.e. the each element has in the base set is ascending.
• Steps will be ordered lexicographic by their indexes into the incoming elements when viewed inverted (from end to start). I.e. a choice of 2 from the string "ABCD" will return
  • "AB"
  • "AC"
  • "BC"
  • "AD"
  • "BD"
  • "CD"
  When you read each result from right to left they are in strict lexical order.

There are various subclasses which take care of combinations of primitive values avoiding boxing and unboxing overhead:

• Combinations.OfRange is the most basic and takes care of combinations of consecutive indices. Indeed all other combinations classes are based on createRangeIterator(int, int) which is used without overhead only by OfRange.
• Combinations.OfInt handle combinations of arbitrary int values.
• Combinations.OfLong handles combinations of arbitrary long values.
• Combinations.OfShort handles combinatons of arbitrary short values.
• Combinations.OfByte handles combinations of arbitrary byte values.
• Combinations.OfDouble handles combinations of arbitrary double values.
• Combinations.OfFloat handles combintaions of arbitrary float values.
• Combinations.OfChar handles combinations of arbitrary char values.
• Combinations.OfString handles combinations of the characters of a java.lang.CharSequence.
• Combinations.OfBoolean handles combintaions of arbitrary byte values.

Since:

November 18, 2021

Author:

Rammi

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	Combinations.OfBoolean Combinations of boolean values.
static class	Combinations.OfByte Combinations of byte values.
static class	Combinations.OfChar Combinations of char values.
static class	Combinations.OfDouble Combinations of double values.
static class	Combinations.OfFloat Combinations of float values.
static class	Combinations.OfInt The combinations of integer values.
static class	Combinations.OfLong Combinations of long values.
static class	Combinations.OfRange The combinations of an index range.
static class	Combinations.OfShort Combinations of short values.
static class	Combinations.OfString The combinations of the characters of a string, as strings.

Constructor Summary

Constructors

Constructor and Description
Combinations(int k, java.util.Collection<T> set) Constructor.
Combinations(int k, Countable<T> set) Constructor.
Combinations(int k, Indexable<T> elements) Constructor.
Combinations(int k, java.util.List<T> list) Constructor.
Combinations(int k, T... elems) Constructor.

Method Summary

Modifier and Type	Method and Description
(package private) static void	checkBinomial(int n, int k) Check the parameters of a "n choice k" for sanity.
static java.math.BigInteger	count(int n, int k) Get the number of combinations for n choose k.
static java.util.Iterator<IntIndexable>	createRangeIterator(int n, int k) Create an iterator which iterates of the subsets of size k from the set {0, 1, 2, ..., n-1}.
java.util.Iterator<Indexable<T>>	iterator()
static void	main(java.lang.String[] args)

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

Constructor Detail

Combinations

public Combinations(int k,
                    @NotNull
                    Indexable<T> elements)

Constructor.

Parameters:

k - number of elements to choose, has to be non-negative and not more the size of the elements set

elements - set from which elements are chosen

Combinations

public Combinations(int k,
                    @NotNull
                    java.util.List<T> list)

Constructor.

Parameters:

k - number of elements to choose, has to be non-negative and not more the size of the list

list - list from which elements will be cosen

Combinations

public Combinations(int k,
                    @NotNull
                    Countable<T> set)

Constructor.

Parameters:

k - number of elements to choose, has to be non-negative and not more the size of the set

set - set from which elements will be chosen

Combinations

public Combinations(int k,
                    @NotNull
                    java.util.Collection<T> set)

Constructor.

Parameters:

k - number of elements to choose, has to be non-negative and not more the size of the set

set - set from which elements will be chosen

Combinations

@SafeVarargs
public Combinations(int k,
                                 @NotNull
                                 T... elems)

Constructor.

Parameters:

k - number of elements to choose, has to be non-negative and not more the number of elements

elems - set from which elements will be chosen

Method Detail

iterator

@NotNull
public java.util.Iterator<Indexable<T>> iterator()

Specified by:

iterator in interface java.lang.Iterable<Indexable<T>>

createRangeIterator

@NotNull
public static java.util.Iterator<IntIndexable> createRangeIterator(int n,
                                                                            int k)

Create an iterator which iterates of the subsets of size k from the set {0, 1, 2, ..., n-1}.

As the latter can be used as indices this iterator can be used as a base for chosing from any set.

Parameters:

n - number of elements in the set from which is chosen

k - number of elements in the chosen sub sets

Returns:

iterator which returns one possible choice from each set, with ordered numbers

checkBinomial

static void checkBinomial(int n,
                          int k)

Check the parameters of a "n choice k" for sanity.

Parameters:

n - n, size of the set from which is chosen

k - k, number of chosen elements

Throws:

java.lang.IllegalArgumentException - if parameters are invalid

count

@NotNull
public static java.math.BigInteger count(int n,
                                                  int k)

Get the number of combinations for n choose k.

Parameters:

n - n, size of the set from which is chosen

k - k, number of chosen elements

Returns:

number of all possible combinations

Throws:

java.lang.IllegalArgumentException - if parameters are invalid

main

public static void main(java.lang.String[] args)