HEADLINE
The Task #1 of Perl Weekly Challenge - 069 raised a very interesting question i.e. is 1 strobogrammatic number? So far, I got mixed response some says yes and some not. My first thought was Yes, it is but later changed my mind. It is controversial and I don’t want loose the focus on the task itself. Please remember the objective is to have fun and not to get into controversial domain. I am also very flexible and not tied to any thing. Some even discussed that “upside down” is not same as “180 degree rotation”. I am staying away from it. I like the open culture of Perl Weekly Challenge as you are free to take the route you are comfortable with. There are no compulsion.
The Task #2 posed another challenge where getting the 0/1 string S1000 generating seems nearly impossible running on regalar machine. Midweek, it was dropped down to S30 to make it possible. Even then it took a long time and generated a very very large 0/1 string.
I have made videos of Live Coding for this week tasks in Perl.
Task #1: Strobogrammatic Number
Task #2: 0/1 String
Let me share my solutions to the Perl Weekly Challenge - 069.
TASK #1 › Strobogrammatic Number
Submitted by Mohammad S Anwar
A strobogrammatic number is a number that looks the same when looked at upside down.
You are given two positive numbers $A and $B such that 1 <= $A <= $B <= 10^15.
Write a script to print all strobogrammatic numbers between the given two numbers.
For the Task #1, I came up with sub strobogrammatic_numbers(), which takes 2-parameters $start and $stop. It assumes, 6, 8 and 9 are the only digits that can be part of any strobogrammatic_numbers. After submitting my solutions, I came to know about 0 being one more such digit. I didn’t bother changing the code. However it would be one-line change if I wanted to include 0 like below.
Replace
my %digits = (6 => 9, 8 => 8, 9 => 6);
with
my %digits = (0 => 0, 6 => 9, 8 => 8, 9 => 6);
and job done.
In the sub below, I loop through $start and $stop. In each loop, I split the number and compare against the keys in the %digits. If I don’t find the split digit in the %digits then I move on the next number in the list. Once all split digits matched with the keys in the %digits, then I compare against the reverse of the mapped digits. If they are same then it is my strobogrammatic number I am after.
sub strobogrammatic_numbers {
my ($start, $stop) = @_;
die "ERROR: Missing start number.\n"
unless defined $start;
die "ERROR: Missing stop number.\n"
unless defined $stop;
die "ERROR: Invalid start number [$start].\n"
unless ($start >= 1);
die "ERROR: Invalid end number [$stop].\n"
unless ($stop >= 1);
die "ERROR: Invalid start number [$start].\n"
unless ($start < $stop);
my %digits = (6 => 9, 8 => 8, 9 => 6);
my @strobogrammatic = ();
foreach my $n ($start .. $stop) {
next if ($n < 10);
my $found = 1;
my @match = ();
foreach my $i (split //, $n) {
if (exists $digits{$i}) {
push @match, $digits{$i};
}
else {
$found = 0;
last;
}
}
if ($found) {
push @strobogrammatic, $n
if ($n == join('', reverse @match));
}
}
return @strobogrammatic;
}
I made controversial assumption in the subroutine above by excluding single digit number. I now realise it is being very rigid. To include single digit should not be too difficult. I can acheive this by dropping the line below:
next if ($n < 10);
Time to get some Raku magic. Thanks to the weekly challenge, I get to practice what I learn in Raku. So what did I learn new? Honestly speaking nothing new but got to practice what I knew already, which is fun as well. I always try my best to make my code not look like Perl.
if %digits{$i}:exists {
For my fellow Perl hacker, the above line checks if $i exists in the hash %digits.
@match.push: %digits{$i};
The line above pushed the mapped digit %digits{$i} to the list @match.
if $n == @match.join('').flip;
Now this compares the number $n with the reverse of the joined digits of the list @match.
I am not sure if you noticed the boolean data True and False used with the variable $found. I love it. I wish Perl had the same.
Please find below the complete definition of sub strobogrammatic-numbers():
sub strobogrammatic-numbers($start, $stop) {
die "ERROR: Invalid start number [$start].\n"
unless $start < $stop;
my %digits = (6 => 9, 8 => 8, 9 => 6);
my @strobogrammatic = ();
for $start .. $stop -> $n {
next if $n < 10;
my $found = True;
my @match = ();
for $n.comb -> $i {
if %digits{$i}:exists {
@match.push: %digits{$i};
}
else {
$found = False;
last;
}
}
if $found {
@strobogrammatic.push: $n
if $n == @match.join('').flip;
}
}
return @strobogrammatic;
}
Let’s solve the task in Perl first with the help of sub strobogrammatic_numbers() we created above.
my $A = $ARGV[0] || 50;
my $B = $ARGV[1] || 100;
print sprintf("[%s]\n", join ', ', strobogrammatic_numbers($A, $B));
How about doing the same in Raku? I love the power of MAIN(), you can do so much with it. I try to put in as much parameter validation as possible in there.
use v6.d;
sub MAIN(Int :$A where { $A >= 1 } = 50,
Int :$B where { $B >= 1 } = 100) {
strobogrammatic-numbers($A, $B).join(', ').say;
}
Being a fan of TDD, I try to get unit test done as well.
use Test::More;
use Test::Deep;
is_deeply( [ strobogrammatic_numbers(50, 100) ],
[ 69, 88, 96 ],
'testing A=50, B = 100' );
Raku unit test is fun as well.
use Test;
is-deeply strobogrammatic-numbers(50, 100),
(69, 88, 96),
'testing $A=50, $B=100';
done-testing;
TASK #2 › 0/1 String
Submitted by Mohammad S Anwar
A 0/1 string is a string in which every character is either 0 or 1.
Write a script to perform switch and reverse to generate S30 as described below:
switch:
Every 0 becomes 1 and every 1 becomes 0. For example, “101” becomes “010”.
reverse:
The string is reversed. For example, "001” becomes “100”.
By the time, I got to do this task, I was already made aware of this task being power hungry.
With that, I didn’t bother getting S1000 generated.
Instead I only attempted to get S30 0/1 string.
The power of tr// made this task so simple.
sub string_0_1 {
my ($string) = @_;
die "ERROR: Missing string.\n"
unless defined $string;
die "ERROR: Invalid string [$string].\n"
unless ($string =~ /s\d+/i);
if ($string =~ /(\d+)/) {
my $limit = $1;
die "ERROR: Invalid string [$string]. S30 is the limit.\n"
if ($limit > 30);
my $string_0_1 = '';
foreach (1 .. $limit) {
my $_string_0_1 = reverse $string_0_1;
$_string_0_1 =~ tr/[01]/[10]/;
$_string_0_1 = '0'. $_string_0_1;
$string_0_1 = $string_0_1 . $_string_0_1;
}
return $string_0_1;
}
}
As you know, I try to translate the Perl solution when it comes to do Raku. I had hard time to find the Raku version of the following line:
if ($string =~ /(\d+)/) {
My Raku regex knowledge is limited, so I google it but couln’t find any solution. At this point, I thought of asking the Raku experts on the @PerlWChallenge twitter handle. Then I found this in the end.
my $limit = .Int for $string ~~ m/(\d+)/;
I am not impressed with the solution, though.
I am sure there must be a better solution out there.
sub string_0_1($string) {
my $limit = .Int for $string ~~ m/(\d+)/;
die "ERROR: Invalid string [$string]. S30 is the limit.\n"
if $limit > 30;
my $string_0_1 = '';
for 1 .. $limit {
my $_string_0_1 = $string_0_1.flip;
$_string_0_1 ~~ tr/[01]/[10]/;
$_string_0_1 = '0' ~ $_string_0_1;
$string_0_1 = $string_0_1 ~ $_string_0_1;
}
return $string_0_1;
}
Time to get the task done in Perl first.
use strict;
use warnings;
my $string = $ARGV[0];
print sprintf("%s\n%s\n", $string, string_0_1($string));
and in Raku now. I love the parameter validation feature of MAIN()
use v6.d;
sub MAIN(Str :$string where { $string ~~ m:i/^s\d+$/ } = 'S5') {
string_0_1($string).say;
}
Quick unit test in Perl, kept it simple.
use Test::More;
is(string_0_1('S2'), '001', 'testing S2');
is(string_0_1('S3'), '0010011', 'testing S3');
is(string_0_1('S4'), '001001100011011', 'testing S4');
done_testing;
Similar unit test in Raku.
use Test;
is string_0_1('S2'), '001', 'testing S2';
is string_0_1('S3'), '0010011', 'testing S3';
is string_0_1('S4'), '001001100011011', 'testing S4';
done-testing;
That’s it for this week. Speak to you soon.