Task — 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.

Try it 

#!/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];
}

Output

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