Robbie Hatley's Solutions, in Perl, for The Weekly Challenge #308 ("Count Common" and "Decode XOR")

For those not familiar with "The Weekly Challenge", it is a weekly programming puzzle with two parts, cycling every Sunday. You can find it here:

The Weekly Challenge

The Weekly Challenge for the week of 2025-02-10 through 2025-02-16 is #308.

The tasks for challenge #308 are as follows:

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Task 308-1: Count Common
Submitted by: Mohammad Sajid Anwar
You are given two array of strings, @str1 and @str2. Write a
script to return the count of common strings in both arrays.

Example #1:
Input: @str1 = ("perl", "weekly", "challenge")
       @str2 = ("raku", "weekly", "challenge")
Output: 2

Example #2:
Input: @str1 = ("perl", "raku", "python")
       @str2 = ("python", "java")
Output: 1

Example #3:
Input: @str1 = ("guest", "contribution")
       @str2 = ("fun", "weekly", "challenge")
Output: 0

For each set of strings I'll make a hash counting occurrences. Then I'll make a (sorted, deduped) "combined" string set from the two originals. Then I'll push any element of @combined which has greater-than-zero occurrences in both original string sets to an array "@common" and return that.

Robbie Hatley's Perl Solution to The Weekly Challenge 308-1

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Task 308-2: Decode XOR
Submitted by: Mohammad Sajid Anwar
You are given an encoded array and an initial integer. Write a
script to find the original array that produced the given
encoded array. It was encoded such that
encoded[i] = orig[i] XOR orig[i + 1].

Example #1:
Input: @encoded = (1, 2, 3), $initial = 1
Output: (1, 0, 2, 1)
Encoded array created like below, if the original array was (1, 0, 2, 1)
$encoded[0] = (1 xor 0) = 1
$encoded[1] = (0 xor 2) = 2
$encoded[2] = (2 xor 1) = 3

Example #2:
Input: @encoded = (6, 2, 7, 3), $initial = 4
Output: (4, 2, 0, 7, 4)

Though the problem description does not specify whether "XOR" refers to "logical XOR" or "bit-wise XOR", the examples make it clear that "XOR" means "the decimal representation of the bit-wise XOR of the binary representations of two small non-negative decimal integers". I say "small" and "non-negative" because otherwise there is no unambiguous meaning to Perl expression "$a ^ $b". So I'll make the stipulation in my program that all numbers involved must be "small non-negative integers in the closed interval [0,255]". In that case, if we let $c = $a ^ $b, then $c ^ $b == $a and $c ^ $a == $b, by the rules of how "XOR" works. So, given the initial (index 0) element of the original, we can then easily recreate the rest of the original by letting each subsequent $orig[i] = $orig[i-1] ^ $encoded[i-1].

Robbie Hatley's Perl Solution to The Weekly Challenge 308-2

That's it for challenge 308; see you on challenge 309!