Task — Sequence number

You are given list of strings in the format aa9999 ie first 2 characters can be anything 'a-z' followed by 4 digits '0-9'.

Write a script to replace the first two characters with sequence starting with '00', '01', '02' etc.

Examples

Example 1
Input: @list = ( 'ab1234', 'cd5678', 'ef1342')
Output: ('001234', '015678', '021342')

Example 2
Input: @list = ( 'pq1122', 'rs3334')
Output: ('001122', '013334')

Analysis

As with many of these tasks, formatting the input to match Mohammad's examples is part - and sometimes most - of the challenge.

The task itself is simply a case of iterating over the supplied list with $j as the index, and replacing each term with:

sprintf('%02d%s', $j, substr($list[$j], 2))

which is the index, left padded with zeroes to make 2 digits, followed by characters 2 (zero-based) to the end of the original string.

Try it 

Script

#!/usr/bin/perl

# Peter Campbell Smith - 2022-09-28
# PWC 184 task 1

use v5.28;
use utf8;
use warnings;

my (@lists, $list_ref, @list, $old_show, $new_show, $j);

# inputs
@lists = (['ab1234', 'cd5678', 'ef1342'], ['pq1122', 'rs3334']);

# loop over inputs
while ($list_ref = shift @lists) {
    @list = @$list_ref;
    $old_show = $new_show = '';

    # loop over list elements
    for $j (0 .. scalar @list - 1) {
        $old_show .= qq['$list[$j]', ];
        $new_show .= qq['] . sprintf('%02d%s', $j, substr($list[$j], 2)) . qq[', ];
    }
    
    # show the answer
    say qq[\nInput:  (] . substr($old_show, 0, -2) . qq[)] .
        qq[\nOutput: (] . substr($new_show, 0, -2) . qq[)];
}

Output

Input:  ('ab1234', 'cd5678', 'ef1342')
Output: ('001234', '015678', '021342')

Input:  ('pq1122', 'rs3334')
Output: ('001122', '013334')