Robbie Hatley's Solutions, in Perl, for The Weekly Challenge #341 (“Broken Keyboard” and “Reverse Prefix”)

For those not familiar with "The Weekly Challenge", it is a weekly programming puzzle with two parts, with a new pair of tasks each Monday. You can find it here: The Weekly Challenge

The Weekly Challenge for the week of 2025-09-29 through 2025-10-05 is #341. The tasks for challenge #341 are as follows:

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Task 341-1: Broken Keyboard
Submitted by: Mohammad Sajid Anwar
You are given a string containing English letters only, and you
are given a list of broken keys. Write a script to return the
total words in the given sentence can be typed completely.

Example #1 input: $str = 'Hello World', @keys = ('d')
Expected output: 1

Example #2 input: $str = 'apple banana cherry', @keys = ('a', 'e')
Expected output: 0

Example #3 input: $str = 'Coding is fun', @keys = ()
Expected output: 3

Example #4 input: $str = 'The Weekly Challenge', @keys = ('a','b')
Expected output: 2

Example #5 input: $str = 'Perl and Python', @keys = ('p')
Expected output: 1

I'll join each "broken key" character and its "shift" (the other character using the same key) into a string "$forbidden", then interpolate $forbidden into a regular-expression character class, then case-insensitively match incoming words against that regexp and push non-matching words to array @allowed, like so:
for (@words) {if ($_ !~ m/[\Q$forbidden\E]/i) {push @allowed, $_}}
I'll then return the scalar of @allowed.

Robbie Hatley's Perl Solution to The Weekly Challenge 341-1

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Task 341-2: Reverse Prefix
Submitted by: Mohammad Sajid Anwar
You are given a string $s and a character $c in $s.
Write a script to reverse the prefix up-to-and-including
the first occurrence of $c in $s and return the new
string.

Example #1 input: $s = "programming", $c = "g"
Expected  output: "gorpramming"

Example #2 input: $s = "hello", $c = "h"
Expected  output: "hello"

Example #3 input: $s = "abcdefghij", $c = "h"
Expected  output: "hgfedcbaij"

Example #4 input: $s = "reverse", $c = "s"
Expected  output: "srevere"

Example #5 input: $s = "perl", $c = "r"
Expected  output: "repl"

To solve this problem, I'll use the little-known scalar version of Perl's built-in "reverse" function, in combination with a "minimal-zero-or-more" regular expression in an "s///re" version of the "s///" substitution operator, like so:
"$s =~ s/^(.*?$c)/reverse($1)/er".

Robbie Hatley's Perl Solution to The Weekly Challenge 341-2

That's it for challenge 341; see you on challenge 342!