use warnings; use strict; use feature 'say';
use MCE::Util;
use MCE::Flow;

sub collatz {
    my ($start) = @_;
    my @seq = $start;
    push @seq, ($seq[-1] / 2, 3 * $seq[-1] + 1)[$seq[-1] % 2]
        while $seq[-1] != 1;
    return @seq;
}

my @sizes;

mce_flow_s {
    max_workers => MCE::Util::get_ncpu(),
    bounds_only => 1,
    gather      => \@sizes,
}, sub {
   my ($mce, $chunk, $chunk_id ) = @_;
   my ($start, $end) = @$chunk;
   my @chunk_sizes;

   push @chunk_sizes, [$_, scalar collatz($_)] for $start .. $end;

   MCE->gather( @chunk_sizes );
}, 1, 1e6;

say "@$_" for reverse +(sort { $b->[1] <=> $a->[1] } @sizes)[0..19];

##</code><code>##

$ time perl ch-map.pl
922525 445
922524 445
906175 445
886953 445
615017 447
410011 449
820023 450
820022 450
818943 450
546681 452
970599 458
796095 468
767903 468
511935 470
927003 476
910107 476
704623 504
939497 507
626331 509
837799 525

real	0m4.843s
user	0m47.423s
sys	0m0.265s

##</code><code>##

time perl ch-flow.pl

922525 445
922524 445
906175 445
886953 445
615017 447
410011 449
820023 450
820022 450
818943 450
546681 452
970599 458
796095 468
767903 468
511935 470
927003 476
910107 476
704623 504
939497 507
626331 509
837799 525

real	0m4.661s
user	0m47.057s
sys	0m0.255s