$ time perl collatz.pl
837799: 525
626331: 509
[lines omitted for brevity]
906175: 445
922524: 445
922525: 445
real 1m37,551s
user 1m9,375s
sys 0m21,031s
####
#!/usr/bin/perl
use strict;
use warnings;
use feature qw/say/;
use constant MAX => 1000000;
my %cache = (2 => 2);
sub collatz_seq {
my $input = shift;
my $n = $input;
my $result = 0;
while ($n != 1) {
if (exists $cache{$n}) {
$result += $cache{$n};
last;
} else {
my $new_n = $n % 2 ? 3 * $n + 1 : $n / 2;
$result++;
$cache{$n} = $cache{$new_n} + 1
if defined $cache{$new_n} and $n < MAX;
$n = $new_n;
}
}
$cache{$input} = $result if $input < MAX;
return $result;
}
my @long_seqs;
for my $num (1..1000000) {
my $seq_length = collatz_seq $num;
push @long_seqs, [ $num, $seq_length ] if $seq_length > 400;
}
@long_seqs = sort { $b->[1] <=> $a->[1]} @long_seqs;
say "$_->[0]: $_->[1]" for @long_seqs[0..19];
##
##
real 0m34,207s
user 0m34,108s
sys 0m0,124s
##
##
#!/usr/bin/perl
use strict;
use warnings;
use feature qw/say/;
use constant MAX => 1000000;
my @cache = (0, 1, 2);
sub collatz_seq {
my $input = shift;
my $n = $input;
my $result = 0;
while ($n != 1) {
if (defined $cache[$n]) {
$result += $cache[$n];
last;
} else {
my $new_n = $n % 2 ? 3 * $n + 1 : $n / 2;
$result++;
$cache[$n] = $cache[$new_n] + 1
if defined $cache[$new_n] and $n < MAX;
$n = $new_n;
}
}
$cache[$input] = $result if $input < MAX;
return $result;
}
my @long_seqs;
for my $num (1..1000000) {
my $seq_length = collatz_seq $num;
push @long_seqs, [ $num, $seq_length ] if $seq_length > 400;
}
@long_seqs = sort { $b->[1] <=> $a->[1]} @long_seqs;
say "$_->[0]: $_->[1]" for @long_seqs[0..19];
##
##
$ time perl collatz3.pl
837799: 525
626331: 509
[Lines omitted for brevity]
922524: 445
922525: 445
real 0m1,755s
user 0m1,687s
sys 0m0,061s