blogs.perl.org

I have been doing Monthly Report since June 2018 non-stop. It has become a ritual for me now. It gives me an opportunity to look upon my activities. Since the beginning of the year 2020, I have made conscious decision to slow down as far as submitting Pull Request. I have also stopped playing CPAN game of daily upload after breaking the chain three times. I am happy that Perlancar is keeping the game alive. It has given me space to try something new. Although COVID-19 keeping us indoor all the time, still looking for interesting project to keep the mind busy.

These are some answers to the Week 97 of the Perl Weekly Challenge organized by Mohammad S. Anwar.

Task 1: Caesar Cipher

You are given string $S containing only the letters A..Z and a number $N.

Write a script to encrypt the given string $S using a Caesar Cipher with left shift of size $N.

Example:

Input: $S = "THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG", $N = 3
Output: "QEB NRFZH YOLTK CLU GRJMP LSBO QEB IXWV ALD"

Plain:    ABCDEFGHIJKLMNOPQRSTUVWXYZ
Cipher:   XYZABCDEFGHIJKLMNOPQRSTUVW

Plaintext:  THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG
Ciphertext: QEB NRFZH YOLTK CLU GRJMP LSBO QEB IXWV ALD

PWC Task #1, Excel Column

jaredor submission for Task #1

Convert back and forth between base 10 and base 26, no problem.

"Column A" equals 1? Problem.

Okay, as problems go, that is a small one. Let I, an old Fortran programmer who loves perl, be your guide between offset indexing and ordinal indexing. First of all, we should complete our assessment of the lay of the land:

"Column 1" equals 1? Problem.

Yes, both column numbering systems start at "one", not "zero", but the mechanical conversion between number bases requires modular arithmetic, which is very much related to offset (0-based) indexing.

Note the quotes? They are meant to emphasize the concept of "one-ness" and "zero-ness" so that I don't have to deal with lexicographic tautologists telling me that "A is A, 1 is 1." Work with me here: The core of difficulty in this task is that we are translating between two number systems that don't have a zero and zero is a big thing.

This is a part of Perl Weekly Challenge(PWC) #060 and the followings are related to my solution. If you want to challenge yourself on Perl, go to https://perlweeklychallenge.org, code the latest challenges, submit codes on-time (by GitHub or email) if possible, before reading my blog post

Do tell me if I am wrong or you strongly oppose my statements!

Task #1: Excel Column

Firstly we observe that 16384 < 26³ = 17576 . Therefore there are at most 3 alphabets for the spreedsheet nomenclature. Knowing the cases to handle are not massive, I handle the cases with some subroutines named AtoOne, AtoZero and OnetoA.

Task #2 Find Numbers

The original task makes me feel it is an exercise for using the module Math::Combinatorics .

Afterall, hence I modify the following more mathematically interesting task for myself:

https://perlweeklychallenge.org/blog/weekly-challenge-062

These are some answers to the Week 96 of the Perl Weekly Challenge organized by Mohammad S. Anwar.

Spoiler Alert: This weekly challenge deadline is due in a couple of days (January 24, 2021). This blog post offers some solutions to this challenge, please don’t read on if you intend to complete the challenge on your own.

Task 1: Reverse Words

You are given a string $S.

Write a script to reverse the order of words in the given string. The string may contain leading/trailing spaces. The string may have more than one space between words in the string. Print the result without leading/trailing spaces and there should be only one space between words.

Example 1:

Input: $S = "The Weekly Challenge"
Output: "Challenge Weekly The"

Example 2:

Input: $S = "    Perl and   Raku are  part of the same family  "
Output: "family same the of part are Raku and Perl"

Reverse Words in Raku

Paging PAWS for fun an profit

Egad have been away for a while, it is not due to laziness on my part, I really have been stuck on a Paws problem over the past month+, add to that dozens of inside and out sided projects that I need to get done around the house time has just not been there.

At least I have finally cracked it.

I really went down a rabbit hole for this one and spend way too many hours trying to figure out how to test 'Paws Pagination' end to end.

In my last post I started out with a new test suite '30_pagination.t' and a few test YAMLs.

Just getting the YAML just right took God only knows how many iterations. I also had to create a completely new caller 'TestPaginationCaller.pm' to get the tests to work.

Excel Column

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.

Example

Input Number: 28
Output: AB

Input Column Name: AD
Output: 30

This seemed like a simple base 10 to base 26 conversion and back. I started by installing Math::Base::Convert, Math::BaseConvert, Math::BaseCnv, and Convert::AnyBase to quickly discover they wouldn’t help me much. What Excel uses for column names is a weird 26 digit system that lacks a symbol for zero, but has a symbol for 26 (or for 10₂₆). It’s called the bijective base-26 numeration system. The interesting fact about such systems is that digit addition, subtraction, and multiplication work the same way as in our common system (division is a bit problematic).

https://perlweeklychallenge.org/blog/weekly-challenge-059

These are some answers to the Week 95 of the Perl Weekly Challenge organized by Mohammad S. Anwar.

Spoiler Alert: This weekly challenge deadline is due in a few of days (January 17, 2021). This blog post offers some solutions to this challenge, please don’t read on if you intend to complete the challenge on your own.

Task 1: Palindrome Numbers

You are given a number $N.

Write a script to figure out if the given number is Palindrome. Print 1 if true otherwise 0.

Example 1:

Input: 1221
Output: 1

Example 2:

Input: -101
Output: 0, since -101 and 101- are not the same.

Example 3:

Input: 90
Output: 0

PWC Task #1, Linked List

jaredor submission for Task #1

Partitioning an input array into a @lower and @upper array based on a pivot element, $k, and then recombining into an output array (@lower, @upper) is pretty easy, e.g.,

say join(' ', (grep { $_ < $k } @ARGV), (grep { $k <= $_ } @ARGV));

A linked list can be collapsed into an array easily enough, so the challenge here (for me) is to add a little extra in the handling that could be useful in the future (because I always steal from myself ;-)

So maybe the little extra is this: Once a link is made it won't be copied.

I started explaining everything and it started feeling like I was writing a very boring novel. Below I'll just stick to the link logic.

Details

Input

There is one command line option:

--k

Specify the pivot point, k, per the problem instructions. [REQUIRED]

The arguments are the elements of the chain, in order, from HEAD to TAIL, since I like to make things as easy for myself as possible.

Link Logic

This is a part of Perl Weekly Challenge(PWC) #059 and the followings are related to my solution. If you want to challenge yourself on Perl, go to https://perlweeklychallenge.org, code the latest challenges, submit codes on-time (by GitHub or email) if possible, before reading my blog post.

(Finally, I installed a Linux distribution in my laptop -- my choice is Linux Mint (a distribution forked from earlier Ubuntu) .) (In Hong Kong, there are no shops selling Linux-installed/Linux-Windows-dual-boot laptop. People^[1] are too rich and just buy Windows pre-installed laptops or MacBooks.(???) ) (This is not my first time to own a laptop with Linux but this time I am more serious about the system setting.)

The COVID-19 virus pandemic is under control in Hong Kong these two week. What a piece of good news.

Perl Weekly Challenge #058

Linked List

You are given a linked list and a value k. Write a script to partition the linked list such that all nodes less than k come before nodes greater than or equal to k. Make sure you preserve the original relative order of the nodes in each of the two partitions.

For example:

Linked List: 1 → 4 → 3 → 2 → 5 → 2
k = 3
Expected Output: 1 → 2 → 2 → 4 → 3 → 5.

We saw Linked List not so long ago, when solving the LRU Cache. Nevertheless, I didn’t reuse my solution, as I previously used a cyclic variant which doesn’t seem to be helpful here.

So, let’s start with a class of list elements. I call them “nodes”. Each node has a value and a link to a next node (undef if there’s none). A node can be disconnected from the next node, or a new node can be attached to it.

These are some answers to the Week 94 of the Perl Weekly Challenge organized by Mohammad S. Anwar.

Spoiler Alert: This weekly challenge deadline is due in a few of days (January 10, 2021). This blog post offers some solutions to this challenge, please don’t read on if you intend to complete the challenge on your own.

Task 1: Group Anagrams

You are given an array of strings @S.

Write a script to group Anagrams together in any random order.

An Anagram is a word or phrase formed by rearranging the letters of a different word or phrase, typically using all the original letters exactly once.

Example 1:

Input: ("opt", "bat", "saw", "tab", "pot", "top", "was")
Output: [ ("bat", "tab"),
          ("saw", "was"),
          ("top", "pot", "opt") ]

Example 2:

Input: ("x")
Output: [ ("x") ]

https://perlweeklychallenge.org/blog/weekly-challenge-058

The last time I spoke at Craft Conference, I also took part in what is probably the most fun and unusual interview of my career: Ivette Ördög’s Morning Commute.

Bear in mind, however, that this discussion took place back in 2018, so you’ll need to mentally s/Perl 6/Raku/ in a couple of places.

Even if you’re not interested in my random thoughts on the importance of linguistic diversity, Ivette’s other interviews are well worth watching.

PWC Task #1, Compare Version

jaredor submission for Task #1

I usually am bored with string twisting (as opposed to bit twiddling) because there is a certain level of grunt work, even with such classics as ELIZA and FESTOON and I can easily fall down the rabbit hole of trying to get pluralization perfect. So when the exciting topic of version numbers came up, I would have passed, but we perfectionists have to finish one to get to two....

Plus there was one thing that I liked, the problem was set up as a comparison operator, like <=> and cmp, suitable for use in a sort routine. Whomever you are out there, with a need to sort thousands of version strings via perl, this script is for you ;-)

Input

Input is on the command line. The versions will be compared in pairs. Creating a version sort routine of command line arguments was considered, but I decided to emulate the problem statement example output instead.

Details

These are some answers to the Week 93 of the Perl Weekly Challenge organized by Mohammad S. Anwar.

Spoiler Alert: This weekly challenge deadline is due in a day or so. This blog post offers some solutions to this challenge, please don’t read on if you intend to complete the challenge on your own.

Task 1: Max Points

You are given set of co-ordinates @N.

Write a script to count maximum points on a straight line when given co-ordinates plotted on 2-d plane.

Example 1:

https://perlweeklychallenge.org/blog/weekly-challenge-060

Compare Version

Compare two given version number strings v1 and v2 such that:

• If v1 > v2 return 1
• If v1 < v2 return -1
• Otherwise, return 0

The version numbers are non-empty strings containing only digits, and the dot (“.”) and underscore (“_”) characters. (“_” denotes an alpha/development version, and has a lower precedence than a dot, “.”). Here are some examples:

v1		v2	Result
0.1	<	1.1	-1
2.0	>	1.2	1
1.2	<	1.2_5	-1
1.2.1	>	1.2_1	1
1.2.1	=	1.2.1	0

When I read the task assignment, I thought to myself: I’m not the first person in the world that needs to compare versions. There already must be a module on CPAN that does exactly that. As usually, it wasn’t so simple.