Permutations: Difference between revisions

There are many modules that can do permutations, or it can be fairly easily done by hand with an example below. In performance order for simple permutation of 10 scalars, a sampling of some solutions:

- 1.7s [https://metacpan.org/pod/Algorithm::FastPermute Algorithm::FastPermute] permute iterator

- 1.7s [https://metacpan.org/pod/Algorithm::Permute Algorithm::Permute] permute iterator

- 2.0s [https://metacpan.org/pod/ntheory ntheory] forperm iterator

- 6.3s [https://metacpan.org/pod/Algorithm::Combinatorics Algorithm::Combinatorics] permutations iterator

- 9.1s the recursive sub below

- 21.1s [https://metacpan.org/pod/Math::Combinatorics Math::Combinatorics] permutations iterator

Example:

} scalar(@tasks);</lang>

</pre>

A simple recursive routine:

<lang perl>sub permutation {

my ($perm,@set) = @_;

print "$perm\n" || return unless (@set);

permutation($perm.$set[$_],@set[0..$_-1],@set[$_+1..$#set]) foreach (0..$#set);

}

my @input = (qw/a 2 c 4/);

permutation('',@input);</lang>

{{out}}

<pre>

a2c4

a24c

ac24

ac42

a42c

a4c2

2ac4

2a4c

2ca4

2c4a

24ac

24ca

ca24

ca42

c2a4

c24a

c4a2

c42a

4a2c

4ac2

42ac

42ca

4ca2

4c2a