use warnings;
use strict;
use ntheory qw/forpart/;
use List::MoreUtils qw/uniq/;

my $sum = shift || 20;
my $terms = shift || 4;

my $amax = $sum;
$amax -= $_ for 1 .. $terms-1;

if ($amax > 0) {
  forpart {
    print "@_\n" if @_ == uniq @_
  } $sum, {n=>$terms, amax=>$amax};
}