Task — 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?'

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 : '') . "'";
}

Output

Input:  'xyz'
Output: 'xyyzzz'

Input:  'hello'
Output: 'heelllllllooooo'

Input:  'challenge'
Output: 'chhaaallllllllleeeeeennnnnnnggggggggeeeeeeeee'

Input:  ''
Output: ''

Input:  'pi=3.14159'
Output: 'pii===3333.....111111444444411111111555555555999
   9999999'