Package org.apache.commons.numbers.combinatorics

Class Combinations

java.lang.Object

org.apache.commons.numbers.combinatorics.Combinations

All Implemented Interfaces:

Iterable<int[]>

public final class Combinations
extends Object
implements Iterable<int[]>

Utility to create combinations (n, k) of k elements in a set of n elements.

Method Summary

Modifier and Type	Method	Description
Comparator<int[]>	comparator()	Creates a comparator.
int	getK()	Gets the number of elements in each combination.
int	getN()	Gets the size of the set from which combinations are drawn.
Iterator<int[]>	iterator()	Creates an iterator whose range is the k-element subsets of {0, ..., n - 1} represented as int[] arrays.
static Combinations	of(int n, int k)	Create an instance.

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

Method Detail

of

public static Combinations of(int n,
                              int k)

Create an instance.

Parameters:

n - Size of the set from which subsets are selected.

k - Size of the subsets to be enumerated.

Returns:

a new instance.

Throws:

IllegalArgumentException - if n < 0.

IllegalArgumentException - if k > n or k < 0.

getN

public int getN()

Gets the size of the set from which combinations are drawn.

Returns:

the size of the universe.

getK

public int getK()

Gets the number of elements in each combination.

Returns:

the size of the subsets to be enumerated.

iterator

public Iterator<int[]> iterator()

Creates an iterator whose range is the k-element subsets of {0, ..., n - 1} represented as int[] arrays.

The iteration order is lexicographic: the arrays returned by the iterator are sorted in descending order and they are visited in lexicographic order with significance from right to left. For example, new Combinations(4, 2).iterator() returns an iterator that will generate the following sequence of arrays on successive calls to next():
[0, 1], [0, 2], [1, 2], [0, 3], [1, 3], [2, 3]

If k == 0 an iterator containing an empty array is returned; if k == n an iterator containing [0, ..., n - 1] is returned.

Specified by:

iterator in interface Iterable<int[]>

comparator

public Comparator<int[]> comparator()

Creates a comparator. When performing a comparison, if an element of the array is not within the interval [0, n), an IllegalArgumentException will be thrown.

Returns:

a comparator.