Re: Combinatorics

[Aristotle]

#!/usr/bin/perl -w
use strict;
use Data::Dumper;

sub unshift_many {
    my $scalar = shift;
    unshift @$_, $scalar for @_;
    @_;
}

sub combinations {
    my ( $array, $len, $start ) = @_;
    $start ||= 0;

    return unless $len > 0;

    return $len == 1
        ? map [ $_ ], @{ $array }[ $start .. $#$array ]
        : map unshift_many( $array->[$_], combinations( $array, $len-1
+, $_+1 ) ),
            $start .. $#$array;
}

$Data::Dumper::Indent=0;
print Dumper( [ combinations [ qw( 1 2 3 4 5 ) ], 3 ] ), "\n";

Makeshifts last the longest.