Alphabet index digit sum

You are given a string $str consisting of lowercase English letters, and an integer $k. Write a script to convert the lowercase string into numbers using alphabet positions (a=1 … z=26), concatenate them to form an integer, then compute the sum of its digits repeatedly $k times, returning the final value.

Examples

Example 1
Input: $str = 'abc', $k = 1
Output: 6
Conversion: a = 1, b = 2, c = 3 -> 123
Digit sum: 1 + 2 + 3 = 6

Example 2
Input: $str = 'az', $k = 2
Output: 9
Conversion: a = 1, z = 26 -> 126
1st sum: 1 + 2 + 6 = 9
2nd sum: 9

Example 3
Input: $str = 'cat', $k = 1
Output: 6
Conversion: c = 3, a = 1, t = 20 -> 3120
Digit sum: 3 + 1 + 2 + 0 = 6

Example 4
Input: $str = 'dog', $k = 2
Output: 8
Conversion: d = 4, o = 15, g = 7 -> 4157
1st sum: 4 + 1 + 5 + 7 = 17
2nd sum: 1 + 7 = 8

Example 5
Input: $str = 'perl', $k = 3
Output: 6
Conversion: p = 16, e = 5, r = 18, l = 12 -> 1651812
1st sum: 1 + 6 + 5 + 1 + 8 + 1 + 2 = 24
2nd sum: 2 + 4 = 6
3rd sum: 6

Analysis

The initial conversion of characters to digits is done using a computed regex:

$a = ord('a') - 1;
$string =~ s|([a-z])|ord($1) - $a|ge;

The repeated summation is done by splitting the numeric string into single digits and summing them.

This is a good example of a solid engineering solution. It shows a structured and clear thinking process, as well as how well you have used the basic features of Perl to accomplish the task at hand. Your implementation is both concise and expressive; thus, demonstrating your mastery of decomposing problems into their components and using clean, idiomatic coding methods in your programming experience.

Try it 

#!/usr/bin/perl

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

use v5.26;    # The Weekly Challenge - 2026-03-16
use utf8;     # Week 365 - task 1 - Alphabet index digit sum
use warnings; # Peter Campbell Smith
binmode STDOUT, ':utf8';
use Encode;

alphabet_index_digit_sum('abc', 1);
alphabet_index_digit_sum('az', 2);
alphabet_index_digit_sum('perl', 3);
alphabet_index_digit_sum('supercalifragilisticexpialidocious', 3);
alphabet_index_digit_sum('', 6);

sub alphabet_index_digit_sum {
    
    my ($string, $count, $a, $sum, @digits, $d);
    
    # initialise
    ($string, $count) = @_;
    $a = ord('a') - 1;
    
    # convert string to digits
    $string =~ s|([a-z])|ord($1) - $a|ge;
    
    # sum repeatedly
    for (1 .. $count) {
        @digits = split(//, $string);
        $string = '';
        $sum = 0;
        $sum += $_ for @digits;
        $string .= $sum;
    }
    
    # report
    say qq[\nInput:  \$str = '$_[0]', \$k = $count];
    say qq[Output: ] . ($sum + 0);
}

13 lines of code

Output from script

Input:  $str = 'abc', $k = 1
Output: 6

Input:  $str = 'az', $k = 2
Output: 9

Input:  $str = 'perl', $k = 3
Output: 6

Input:  $str = 'supercalifragilisticexpialidocious', $k = 3
Output: 10

Input:  $str = '', $k = 6
Output: 0