javagl / Combinatorics

Utilities for combinatorics

Combinatorics

Utility classes for combinatorics.

General information

The classes in this library are mainly intended as small utility classes and demo cases for various combinatorial computations. The focus is on simplicity, understandability and ease of use. They are not intended as a "combinatorics framework", but merely as a quarry for code snippets.

Each kind of combinatorial computation that is offered by these classes comes as an Iterable. Thus, they can easily be used in foreach loops. They usually expect their input as a List, and provide combinations of elements as new Lists.

Example:

List<String> input = Arrays.asList("A", "B", "C");
PermutationIterable<String> permutationIterable = 
    new PermutationIterable<String>(input);
for (List<String> permutation : permutationIterable)
{
    System.out.println(permutation);
}

Output:

[A, B, C]
[A, C, B]
[B, A, C]
[B, C, A]
[C, A, B]
[C, B, A]

Each class contains a JavaDoc class comment explaining what it actually computes, and an example showing the input and output.

An advantage of offering the computation results via an Iterable is that the result can be computed on the fly. However, when a collection with all resulting elements is required, such a collection can be created using one of the methods in the Utils class.

Example:

List<String> input = Arrays.asList("A", "B", "C");
List<List<String>> permutations =
    Utils.asList(new PermutationIterable<String>(input));