Changing keys

You are given an alphabetic string $str as typed by user. Write a script to find the number of times user had to change the key to type the given string. Changing key is defined as using a key different from the last used key. The shift and caps lock keys won’t be counted.

Examples

Example 1
Input: $str = 'pPeERrLl'
Output: 3
p -> P : 0 key change
P -> e : 1 key change
e -> E : 0 key change
E -> R : 1 key change
R -> r : 0 key change
r -> L : 1 key change
L -> l : 0 key change

Example 2
Input: $str = 'rRr'
Output: 0

Example 3
Input: $str = 'GoO'
Output: 1

Analysis

As in task 1, I could not see an obvious way to do this with a single regular expression, but this time, lower-casing the string and then comparing successive pairs of characters is relatively easy.

But I'm sure the RE experts will have found a better way.

Plenty to discuss about the issues faced with regex when using Perl and in the end the work around. Well done and keep it up.

This review may cover either or both challenges for this week.

I am sorry that the 'Try it' feature is currently working very slowly or not at all owing to some issue with my web hosting provider.

Try it 

Try running the script with any input:

Your $str =

example: The Weekly Challenge

⤡

#!/usr/bin/perl

# Blog: http://ccgi.campbellsmiths.force9.co.uk/challenge

use v5.26;    # The Weekly Challenge - 2024-08-12
use utf8;     # Week 282 - task 2 - Changing keys
use warnings; # Peter Campbell Smith
binmode STDOUT, ':utf8';

changing_keys('aaabbbcCc');
changing_keys('abbbbb');
changing_keys('aaaaab');
changing_keys('abcde');
changing_keys('aAaAaAa');
changing_keys('Committee');

sub changing_keys {
    
    my ($str, $c, $count);
    
    # initialise
    $str = shift;
    say qq[\nInput:  \@str = '$str'];
    
    # count key changes
    $str = lc($str);
    $count = 0;
    for $c (0 .. length($str) - 2) {
        $count ++ if substr($str, $c, 1) ne substr($str, $c + 1, 1);
    }
    say qq[Output: $count];
}

9 lines of code

Output from script

Input:  @str = 'aaabbbcCc'
Output: 2

Input:  @str = 'abbbbb'
Output: 1

Input:  @str = 'aaaaab'
Output: 1

Input:  @str = 'abcde'
Output: 4

Input:  @str = 'aAaAaAa'
Output: 0

Input:  @str = 'Committee'
Output: 5