#!/usr/bin/perl
use strict;
use warnings;

my @list1 = 1 .. 5;
my @list2 = 1 .. 5;

my @merge_list = ((0) x scalar @list1); # use smaller of 2 lists 

while (1) {
    my ($min, $idx);
    for (my $i = 0; $i < @merge_list; ++$i) {
        next if $merge_list[$i] > $#list2;
        my $sum = $list1[$i] + $list2[$merge_list[$i]];
        ($min, $idx) = ($sum, $i) if ! defined $min || $sum < $min;
    }
    last if ! defined $min;
    print "$min\n";
    $merge_list[$idx]++;
}