http://www.perlmonks.org?node_id=355455

Solo has asked for the wisdom of the Perl Monks concerning the following question:

I'm using a stack algorithm to solve a combinatorial problem--and I'm out of my comfort zone. This simplified example finds the subsets of a set of integers whos sum is a target number.

Searches on 'perl perl stack' or 'perl perl subset' proved rather off-topic, and 'combinatorial algorithm' was way out there. So I'm hoping for some constructive criticism here. For starters, is there a better/faster than brute-force algorithm? Or how about a more Perlish implementation? I feel like a C programmer ;p

Here's the code I'm using now.

```use strict;

my @block  = qw/ 1 2 3 4 5 6 7 8 9 /;
my \$target = 20;

my @solutions = solve(\$target,@block);
print join(',',@\$_) . "\n" for ( @solutions );

# find all combinations of blocks that sum to target
sub solve {
my ( \$target, @block ) = @_;
my ( @solutions, @trial, @stack );
my \$acc = -1;

NEW: while (1) {
if ( sum( \@trial ) == \$target ) {
my @solu = @trial;
push @solutions, \@solu;
}
OLD: while (1) {
\$acc++;
if ( \$acc <= \$#block ) {
push @trial, \$block[\$acc];
push @stack, \$acc;
next NEW;
}
elsif (@stack) {
pop @trial;
\$acc = pop @stack;
next OLD;
}
else { last NEW }
}
}

return @solutions;
}

sub sum {
local \$_;
my (\$array) = @_;
my \$sum;
\$sum += \$_ for (@\$array);
return \$sum;
}