$ perl 11105885.pl
$buckets = [
             [
               '1',
               '5',
               '9'
             ],
             [
               '2',
               '6',
               '10'
             ],
             [
               '3',
               '7',
               '11'
             ],
             [
               '4',
               '8',
               '12'
             ]
           ];