combinations

README

Golang combinations

This package provides a method to generate all ordered combinations out of a given string array. This essentially creates the powerset of the given array except that the empty set is disregarded.

Examples

Take a look at the godoc for examples.

In general when you have e.g. []string{"A", "B", "C"} you will get:

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

Background

The algorithm iterates over each number from 1 to 2^length(input), separating it by binary components and utilizes the true/false interpretation of binary 1's and 0's to extract all unique ordered combinations of the input slice.

E.g. a binary number 0011 means selecting the first and second index from the slice and ignoring the third and fourth. For input {"A", "B", "C", "D"} this signifies the combination {"A", "B"}.

For input slice {"A", "B", "C", "D"} there are 2^4 - 1 = 15 binary combinations, so mapping each bit position to a slice index and selecting the entry for binary 1 and discarding for binary 0 gives the full subset as:

1	=	0001	=>	---A	=>	{"A"}
2	=	0010	=>	--B-	=>	{"B"}
3	=	0011	=>	--BA	=>	{"A", "B"}
4	=	0100	=>	-C--	=>	{"C"}
5	=	0101	=>	-C-A	=>	{"A", "C"}
6	=	0110	=>	-CB-	=>	{"B", "C"}
7	=	0111	=>	-CBA	=>	{"A", "B", "C"}
8	=	1000	=>	D---	=>	{"D"}
9	=	1001	=>	D--A	=>	{"A", "D"}
10	=	1010	=>	D-B-	=>	{"B", "D"}
11	=	1011	=>	D-BA	=>	{"A", "B", "D"}
12	=	1100	=>	DC--	=>	{"C", "D"}
13	=	1101	=>	DC-A	=>	{"A", "C", "D"}
14	=	1110	=>	DCB-	=>	{"B", "C", "D"}
15	=	1111	=>	DCBA	=>	{"A", "B", "C", "D"}

Documentation

Overview

Package combinations provides a method to generate all combinations out of a given string array.

Index

• func All[T any](set []T) (subsets [][]T)
• func Combinations[T any](set []T, n int) (subsets [][]T)

Examples

• All

Functions

func All

func All[T any](set []T) (subsets [][]T)

All returns all combinations for a given string array. This is essentially a powerset of the given set except that the empty set is disregarded.

Example

combinations := All([]string{"A", "B", "C"})
fmt.Println(combinations)

Output:

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

func Combinations

func Combinations[T any](set []T, n int) (subsets [][]T)

Combinations returns combinations of n elements for a given string array. For n < 1, it equals to All and returns all combinations.