Here is a quick and dirty version that doesn't generate all combinations and then filter, but only does the strictly needed work (I assume the array elements have length 1):
#!/usr/bin/perl -wl
use strict;
print for generate(4,
[qw(a b c)], [qw(d e)], [qw(f g h)], ["i"],
[qw(j k)], ["l"], ["m"]);
sub generate {
my $min = shift;
my @non_empty = grep @$_, @_;
return if $min > @non_empty;
work($min, @non_empty);
}
sub work {
my $min = shift;
return "" if !@_;
my $first = shift;
return map {
my $n = $_;
length() < $min ? () : $_, map $_.$n, @$first;
} work($min-1, @_);
}
update: A purely iterative version of the above:
sub generate {
my $min = shift;
my @arrays = grep @$_, @_;
$min -= @arrays;
return if $min > 0;
my @current = ("");
for my $array (@arrays) {
$min++;
@current = map {
my $n = $_;
length() < $min ? () : $_, map $n.$_, @$array;
} @current;
}
return @current;
}