use strict; use warnings; use feature qw/say/; use constant MAX => 300000; use MCE::Util; use MCE::Map max_workers => MCE::Util::get_ncpu(); use Time::HiRes qw/usleep/; my %cache; sub collatz_seq { my $input = shift; my $n = $input; my @result; while ($n != 1) { if (exists $cache{$n}) { push @result, @{ $cache{$n} }; last; } my $new_n = $n % 2 ? 3 * $n + 1 : $n / 2; usleep 20; # simulate extra computation push @result, $new_n; $cache{$n} = [ $new_n, @{ $cache{$new_n} } ] if $n < MAX && exists $cache{$new_n}; $n = $new_n; } $cache{$input} = \@result if $n < MAX; return @result; } my @long_seqs = mce_map_s { my $num = $_; my @seq = ($num, collatz_seq $num); return [ $num, scalar @seq ]; } 1, 100000; MCE::Map->finish; @long_seqs = sort { $b->[1] <=> $a->[1] } @long_seqs; say "$_->[0] : length $_->[1]" for @long_seqs[0..19];