Advent Calendar 2023

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The gift is presented by Simon Green. Today he is talking about his solution to The Weekly Challenge - 220. This is re-produced for Advent Calendar 2023 from the original post.

Common Squares

Weekly Challenge 220

This is the second consecutive week I’ve done the task and written the blog 40,000+ feet in the air.

Task 1: Common Characters

You are given a list of words.

Write a script to return the list of common characters (sorted alphabetically) found in every word of the given list.

My solution

[   Perl   |   Python   ]

These are the steps I took.

1. From a list (array in Perl) of words, I create a list called set_list. Each item is a set (hash in Perl) of the lower case letters that occur in each word. In Python this is achieved using set(word) as strings are an iterable. In Perl I have a function called word_to_hash as it seemed like a bit too much to stuff into a single map statement.

2. I take off the first word from the set_list and assign it to the first_word variable.

3. I loop through each letter in the first word alphabetically.

4. I check that the letter is indeed a letter from the English alphabet and that it appears in all the words in the set_list list. If it is, I append it to the letters list.

5. Finally, I print items in the letters list.

Examples

$ ./ch-1.py Perl Raku Rust
r

$ ./ch-1.py love live leave
e, l, v

Task 2: Squareful

You are given an array of integers, @ints.

An array is squareful if the sum of every pair of adjacent elements is a perfect square.

Write a script to find all the permutations of the given array that are squareful.

My solution

[   Perl   |   Python   ]

Rather than reinventing some perfectly good wheels, I use the permutation function from Python's itertools and Perl's Algorithm::Combinatorics to work through all possible permutations. If we already have a solution with these numbers (e.g. a duplicate number), we skip to the next permutation.

I then have an inner loop from 1 to one less than the number of integers we have. I check that the value at that position and the previous position makes up a perfect square. This is done by calculating the square root of the sum of the two numbers, and checking it is equals to an integer.

Examples

$ ./ch-2.py 1 17 8
(1, 8, 17), (17, 8, 1)

$ ./ch-2.py 2 2 2
(2, 2, 2)

If you have any suggestion then please do share with us perlweeklychallenge@yahoo.com.

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