use strict;
use warnings;

my @vals = (1, 2, 3, 4, 5);
my $n = 3;
my @solutions;

nSum(\@vals, \@solutions, 0, -1, $n);

print "@solutions\n";

sub nSum {
    my ($vals, $solutions, $sum, $i, $n) = @_;

    if (--$n) {
        nSum($vals, $solutions, $sum + $vals->[$_], $_, $n)
            for ($i+1)..$#$vals;
    }
    else {
        push @$solutions, $sum + $vals->[$_]
            for ($i+1)..$#$vals;
    }
}