Echo chamber

You are given a string containing lowercase letters. Write a script to transform the string based on the index position of each character (starting from 0). For each character at position i, repeat it i + 1 times.

Examples

Example 1
Input: 'abca'
Output: 'abbcccaaaa'
Index 0: 'a' -> repeated 1 time  -> 'a'
Index 1: 'b' -> repeated 2 times -> 'bb'
Index 2: 'c' -> repeated 3 times -> 'ccc'
Index 3: 'a' -> repeated 4 times -> 'aaaa'

Example 2
Input: 'xyz'
Output: 'xyyzzz'
Index 0: 'x' -> 'x'
Index 1: 'y' -> 'yy'
Index 2: 'z' -> 'zzz'

Example 3
Input: 'code'
Output: 'coodddeeee'
Index 0: 'c' -> 'c'
Index 1: 'o' -> 'oo'
Index 2: 'd' -> 'ddd'
Index 3: 'e' -> 'eeee'

Example 4
Input: 'hello'
Output: 'heelllllllooooo'
Index 0: 'h' -> 'h'
Index 1: 'e' -> 'ee'
Index 2: 'l' -> 'lll'
Index 3: 'l' -> 'llll'
Index 4: 'o' -> 'ooooo'

Example 5
Input: 'a'
Output: 'a'
Index 0: 'a' -> 'a'

Analysis

You can do this in a one-liner:

$output .= substr($input, $_, 1) x ($_ + 1) 
   for 0 .. length($input) - 1;

but I felt it was clearer to split the input into @chars, and then the line that does the work is easier to understand.

I might be forgiven for thinking 'Why would you ever need to do that?'

This challenge page from Peter presents the Perl Weekly Challenge 362 tasks with clear problem statements for both 'Echo Chamber' and 'Spellbound Sorting'. It provides a solid foundation for exploring string manipulation and sorting by word form, making it a useful resource for practicing concise algorithm design in Perl.

Try it 

#!/usr/bin/perl

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

use v5.26;    # The Weekly Challenge - 2026-02-23
use utf8;     # Week 362 - task 1 - Echo chamber
use warnings; # Peter Campbell Smith
binmode STDOUT, ':utf8';
use Encode;

echo_chamber('xyz');
echo_chamber('hello');
echo_chamber('challenge');
echo_chamber('');
echo_chamber('pi=3.14159');

sub echo_chamber {
    
    my ($input, @chars, $output);
    
    # just do it
    @chars = split('', $_[0]);
    $output .= $chars[$_] x ($_ + 1) for 0 .. $#chars;
        
    say qq[\nInput:  '$_[0]'];
    say qq[Output: '] . (defined $output ? $output : '') . "'";
}

6 lines of code

Output from script

Input:  'xyz'
Output: 'xyyzzz'

Input:  'hello'
Output: 'heelllllllooooo'

Input:  'challenge'
Output: 'chhaaallllllllleeeeeennnnnnnggggggggeeeeeeeee'

Input:  ''
Output: ''

Input:  'pi=3.14159'
Output: 'pii===3333.....1111114444444111111115555555559999999999'