jarich

My starting problem is easy. Coming from Project Euler:

If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.

Find the sum of all the multiples of 3 or 5 below 1000.

Perl 5:

use v5.14.2;
use strict;
use warnings;
use autodie;

# We want all the factors lower than this number.
my $max = (shift || 1000) - 1;

# Collect all of the multiples into a hash. (We'd use an array, but this is
# faster to making sure that we don't double up)
my %multiples;

foreach my $factor (5, 3) {
    # Find our first multiple
    my $start = $max - ( $max % $factor );

    # Now just add each factor until zero (skipping ones already added)
    while( $start > 0 ) {
        unless( $multiples{$start} ) {
            $multiples{$start}++;
        }
        $start -= $factor;
    }
}

# Print multiples and the total.
say "My multiples are: ", join " ", sort { $a <=> $b } keys %multiples;

my $total;
$total += $_ for keys %multiples;
say "total: $total";

Not much to say about that solution. I could calculate the total as I'm adding things into the hash and thus not have to walk over it at the end, I could (of course) put the magic numbers into variables, but it's a fairly standard approach. Perl 5.14.2 is what I have on my machine.

The perl5i solution is much the same:

use perl5i::2;

# We want all the factors lower than this number.
my $max = (shift || 1000) - 1;

# All of our multiples
my @multiples;

foreach my $factor (5, 3) {
    # Find our first multiple
    my $start = $max - ( $max % $factor );

    # Now just add each factor until zero (skipping ones already added)
    while( $start > 0 ) {
        unless( @multiples->first(sub {$_ $start} ) ) {
           @multiples->push($start);
        }
        $start -= $factor;
    }
}

# Print multiples and the total.
my @sorted = sort { $a <=> $b } @multiples;
say "My multiples are: ", @sorted->join(" ");

#say "My multiples are: ", @multiples->sort( sub { $[0] <=> $[1]} )->join(" ");

my $total;
$total += $_ for @multiples;
say "total: $total";

I really wanted to use the sort->join->say kind of chaining, but I think the sub for the sort block is ugly. The sub for first is pretty annoying too.

Perl 6:

use v6;

# We want all the factors lower than this number.
sub MAIN($max = 1000) {

    # All of my multiples.
    my @multiples;

    for (5, 3) -> $factor {
        # Find our first multiple
        my $start = $max - ( $max % $factor );

        # Now just add each factor until zero (skipping ones already added)
        while $start > 0  {
            unless any(@multiples) $start {
               @multiples.push($start);
            }
            $start -= $factor;
        }
    }

    # Print multiples and the total.
    say "My multiples are: ", @multiples.sort({$a <=> $b}).join(" ");

    my $total;
    $total += $_ for @multiples;
    say "total: $total";
}

It took me a little while to find MAIN, but if that's how I have to process command line arguments, so be it. The rest was pretty straight forward after some initial confusions about any() and the sort block for a while.

Time Comparisons:

jarich@blackberry:~/polyglot$ time perl multiples35.pl 20
My multiples are: 3 5 6 9 10 12 15 18
total: 78

real    0m0.117s
user    0m0.100s
sys    0m0.016s

jarich@blackberry:~/polyglot$ time perl5i multiples35.p5i 20
My multiples are: 3 5 6 9 10 12 15 18
total: 78

real    0m0.651s
user    0m0.608s
sys    0m0.040s

jarich@blackberry:~/polyglot$ time perl6 multiples35.p6 20
My multiples are: 3 5 6 9 10 12 15 18 20
total: 98
real    0m8.910s
user    0m8.685s
sys    0m0.148s

Not a real benchmark, but Perl 6 is noticably slower.

PS: Any hints on getting the syntax highlighting available in code blocks to work in blockcode in any of the available editors very gratefully appreciated.

UPDATE: Thanks to Ovid, I found to get the formatting I wanted, I needed to use the Markdown editor, and then the indentation I had.