HEADLINE

I am not sure about you guys but I found writing blog is very nice feeling. I get nice ideas to clean up the code. This week, I even found a bug that even unit test couldn’t catch. I would rather not share it, quite embarassing. The bug was in my Perl solutions to the “Find Numbers” task. My git commit tree might disclose it, if you really want to know.

Back to the weekly challenges, I liked both tasks and I finished the Perl solutions to both task on day one i.e.Monday itself. Generally I go slow on Monday and Tuesday to recover from the weekend hangover, the most busiest time of the week because of Perl Weekly Challenge and Perl Weekly Newsletter. When I am editing the Perl Weekly Newsletter then it is double whammy for me. I am glad that I only edit alternate week. So I get a breather in between.

Once I am done with Perl solutions, I find myself little relax as I know I can easily get the Raku version quickly. Because of my fasting, I find it hard to do any coding during the day. After breaking the fast, I feel sleepy and take quick couple of hours of nap break. I then wake up midnight to perform night prayer and eat the Sehar. It is the time after morning prayer, I find myself full of energy. On saturday morning after prayer at 3:20 am, I started preparing the ground for Raku solutions. By 10:00 am, I had both the tasks done. Not a bad attempt. I did throw few questions when I was struck at one point. I will talk about it in detail later.

Since I started working from home, my daily routine has gone upside down. During the Ramadan, my office working hours is 8:00 am to 3:30 pm without lunch break, obviously. From 3:30 pm to 8:50 pm (time of breaking fast), is for me to perform regular prayer and relax. Sometimes I watch movie on Netflix. Couple of days ago, I watched 6 Days, nice movie. Before that I watched Bodyguard. I am new to Netflix and therefore most of the movies are new to me.

Enough of my story, let me share my solutions to the Perl Weekly Challenge - 060.

TASK #1 › Excel Column

Reviewed by Ryan Thompson

Write a script that accepts a number and returns the Excel Column Name it represents and vice-versa.

Excel columns start at A and increase lexicographically using the 26 letters of the English alphabet, A..Z. After Z, the columns pick up an extra “digit”, going from AA, AB, etc., which could (in theory) continue to an arbitrary number of digits. In practice, Excel sheets are limited to 16,384 columns.

For this task, I was tempted to find a solution on CPAN. But then I changed my mind and decided to bring the kid inside me to do the hard way. It reminded me of my early days of learning Perl5, I think it was in the year 1998. I kept the logic simple and easy to follow. I applied the pattern, I learnt during my college days when we were asked to convert Decimal to Binary and vice-versa.

I read some of the blogs by fellow Team PWC members, I don’t remember who, talking about the complexity dealing with it. I didn’t come across any during my investigation. May be, my solution has some hidden bugs that I am not aware of it. If you do come across please let me know.

During the initial draft, I decided to have two subroutines sub from_excel() and sub to_excel(). But then I changed my mind after completing the Raku solution for the same task where I just defined one sub excel-column(). It wasn’t difficult to merge the two. Just added the parameter checking regex then everything was in place.

I would like to point out one mystery that I came across when trying to reverse the string i.e. reverse(uc $arg). It wasn’t giving me the expected result for some unknown reason. I had to do scalar(reverse(uc $arg)) to get the desired result. It could be I am missing something very basic. Please do share with me if you know the reason.

sub excel_column {
    my ($arg) = @_;

    if ($arg =~ /^\d+$/) {
        my $name = '';
        my @name = (0, 'A' .. 'Z');
        while ($arg > 26) {
            my $i = int $arg / 26;
            $name .= $name[$i];
            $arg  -= ($i * 26);
        }
        $name .= $name[$arg];

        return $name;
    }
    elsif ($arg =~ /^[A-Z]+$/i) {
        my $i = 0;
        my $b = 26;
        my $d = 0;
        foreach my $c (split //, scalar(reverse(uc $arg))) {
            $d += (ord($c) - ord("A") + 1) * ($b ** $i++);
        }

        return $d;
    }
    else {
        die "ERROR: Invalid column [$arg].\n";
    }
}

Time to do some Raku magic, when I defined two subs for Perl solution, I thought I would use multi sub feature of Raku. It is one of my favourite features of Raku. So when I said “I defined one sub excel-column() earlier …", techically I defined two with multi sub, so in a way it is cheating.

The benefit of having the solution ready, It is easier to think of Raku way of dealing with it. It didn’t take long to convert the following line in Perl:

foreach my $c (split //, scalar(reverse(uc $arg))) {

to Raku equivalent like below:

for $name.uc.flip.comb -> $c {

Don’t you think, it is beautiful?

I did this in my head, for a change. Normally I do hit and run process. When it works, I make a note of it for future.

multi sub excel-column(Str $name) {

    my $i = 0;
    my $b = 26;
    my $d = 0;

    for $name.uc.flip.comb -> $c {
        $d += ($c.ord - "A".ord + 1) * ($b ** $i++);
    }

    return $d;
}

Let us talk about the other half. Couple of things, I struggled here.

First, I tried to convert the following line in Perl:

my @name = (0, 'A' .. 'Z');

I am sure, there are plenty of ways dealing with it in Raku. With my limited knowledge, I thought the same line would work in Raku. Guess what, like always, I was wrong.

When I did the same in Raku, the second element of @name had all the alphabets instead of one in each cell. So I decided to take the shortcut, I know it is not nice but does the job. If you know better way then please do let me know.

my @name = 'A'..'Z';
@name.unshift(0);

The second hurdle I faced when trying to convert the following line in Perl:

my $i = int $arg / 26;

Again, I thought the same line would work in Raku. I was wrong once again. Looked around documentation and I found this.

my $i = $number div 26;

Is it correct way of dealing with it?

Rest of the solution was simple straight forward.

multi sub excel-column(Int $number is copy) {

    my $name = '';
    my @name = 'A'..'Z';
    @name.unshift(0);

    while $number > 26 {
        my $i = $number div 26;
        $name   ~= @name[$i];
        $number -= $i * 26;
    }
    $name ~= @name[$number];

    return $name;
}

After doing all the hard work, the end result becomes a matter of few lines.

Don’t you love thin wrapper?

my $arg = $ARGV[0];
die "ERROR: Please provide parameter e.g. AA or 27.\n"
    unless defined $arg;

print sprintf("%s => %s\n", $arg, excel_column($arg));

Raku with multi sub MAIN() is elegant as well.

I also love the <cond> ?? <exp> !! <exp> construct. I use it whenever I get the opportunity.

use v6.d;

multi sub MAIN(*@) is hidden-from-USAGE {
    say $*USAGE;
}

multi sub MAIN(Str :$name?, Int :$number?) {
    die "ERROR: Missing --name=<Str> or --number=<Int>.\n"
        unless defined $name or defined $number;

    defined $name
    ??
    say sprintf("%s => %s", $name, excel-column($name))
    !!
    say sprintf("%s => %s", $number, excel-column($number.Int));
}

The benefit of having just one sub excel_column, the unit test code looks cleaner.

use Test::More;

is (excel_column("Z"),  26,  "Z  => 26");
is (excel_column("AB"), 28,  "AB => 28");
is (excel_column(28),  "AB", "28 => AB");

done_testing;

The same applied to Raku as well. They both look so identical. I am amazed.

use Test;

is excel-column('Z'),  26, 'Z  => 26';
is excel-column('AB'), 28, 'AB => 28';
is excel-column(28), 'AB', '28 => AB';

done-testing;

TASK #2 › Find Numbers

Reviewed by Ryan Thompson

Write a script that accepts list of positive numbers (@L) and two positive numbers $X and $Y.

The script should print all possible numbers made by concatenating the numbers from @L, whose length is exactly $X but value is less than $Y.

For this task, once again, I took the help from CPAN module Algorithm::Combinatorics. But this time I used sub variations_with_repetition() because we wanted variations with repetition. After that there wasn’t anything left to do, to be honest.

use Algorithm::Combinatorics qw(variations_with_repetition);

sub find_numbers {
    my ($n, $x, $y) = @_;

    my @numbers = ();
    foreach my $number (variations_with_repetition($n, $x)) {
        $number = join("", @$number) + 0;
        next unless ((length($number) == $x) && ($number < $y));
        push @numbers, $number;
    }

    return @numbers;
}

But for Raku, I was not aware of any such module. So I decided to get my hand dirty and in the process learnt few tricks. Not a bad choice.

First I tried @numbers.combinations(2) which didn’t give me the expected pairs:

> say <0 1 2 5>.combinations(2);
((0 1) (0 2) (0 5) (1 2) (1 5) (2 5))
>

I was specially interested in pairs like (1 1) (2 2) (3 3).

Once again after trying all the tricks from my notes, I wasn’t going anywhere. So I decided to throw the questions at the @PerlWChallenge twitter handle. While I was waiting for the response, I kept trying few things.

Then suddenly it clicked and got the solution.

> say <0 1 2 5> X <0 1 2 5>;
((0 0) (0 1) (0 2) (0 5) (1 0) (1 1) (1 2) (1 5) (2 0) (2 1) (2 2) (2 5) (5 0) (5 1) (5 2) (5 5))
>

I did receive different solutions from the experts but I liked mine. It is simple and easy to remember.

The next challenge was to join both integers from the pair and deal with pair having 0 as first integer.

To join the pair elements, my note came handy this time.

my $number = [~] @x;

To get rid of 0, I simply used the trick from Perl.

my $number = ([~] @x) + 0;

Rest of the code was nothing new to me.

sub find-numbers(@n, $x, $y) {

    my @numbers = ();
    for @n X @n -> @x {
        my $number = ([~] @x) + 0;
        next unless $number.chars == $x && $number < $y;
        @numbers.push: $number;
    }

    return @numbers;
}

Now the fun part, creating standalone app becomes piece of cake.

my @numbers = find_numbers([0, 1, 2, 5], 2, 21);
print join(", ", @numbers), "\n";

Raku solution has some default parameters and type checking for fun.

Other than that, it is pretty straight forward.

sub MAIN(:@n where .all ~~ Int = <0 1 2 5>, Int :$x = 2, Int :$y = 21) {

    my @numbers = find-numbers(@n, $x, $y);
    say @numbers.join(", ");
}

To make it complete solution, here is basic unit test. Nothing great.

use Test::More;

my @numbers = find_numbers([0, 1, 2, 5], 2, 21);
is (join(", ", @numbers), "10, 11, 12, 15, 20");

done_testing;

Raku is even slimmer as always.

use Test;

is-deeply find-numbers(<0 1 2 5>, 2, 21), [10, 11, 12, 15, 20];

done-testing;

That’s it for this week. Speak to you soon.