http://qs321.pair.com?node_id=554374

I have a text string which contains a sequence of words. For example:
horse:cow:dog:cat
I needed to generate every combination of words (missing or not), but each combination must maintain the original sequence. For example a partial result of the above:
cow, cat, horse:cow, horse:cat, cow:dog:cat, etc
(cow:horse would be considered out of sequence)
Here's how I handled it. Perhaps there's a faster way?
use strict; use warnings; # initial source in sequence order my $source = 'horse:cow:dog:cat'; # hash used to store results (weed out dups) my %hash; function(\%hash, $source); # and now the results foreach (keys %hash) { print "$_\n"; } # generate array of combinations # (hash keys are the results) sub function { my $hash_ref = shift; my $source = shift; # skip it if we've been here return if $hash_ref->{$source}; $hash_ref->{$source}++; # remove one of each part from the whole if ((my @parts = split(/:/, $source)) > 1) { for (my $i = 0; $i < @parts; $i++) { my @parts_copy = split(/:/, $source); splice(@parts_copy, $i, 1); function($hash_ref, join(':',@parts_copy)); } } return; }