#!/usr/local/bin/perl
use strict;
use warnings;

my $foo = 'abbcccddddeeeeeffffffggggggghhhhhhhhiiiiiiiii'
    . 'jjjjjjjjjj122333444455555666666777777788888888999999999!';

for my $longest ( 1 .. 5 ) {
    my $bar = max_run_1 ( $longest, $foo );
    print 'max_run_1: ' . $bar . "\n";
    $bar = max_run_2 ( $longest, $foo );
    print 'max_run_2: ' . $bar . "\n";
}


sub max_run_1 {
    my $max = $_[0];
    my $len = length $_[1];

    ### loop prelude
    my $char = substr $_[1], 0, 1;
    my $count = 1;
    my $new_string = $char;
    my $at = 1;

    while ( $at < $len ) {
        my $old_char = $char;
        $char = substr $_[1], $at++, 1;

        if ( $char eq $old_char ) {
            next if $count >= $max;
            $count++;
        } else {
            $count = 1;
        }
        $new_string .= $char;
    }

    return $new_string;
}

sub max_run_2 {
    my $max = $_[0];
    ( my  $new_string = $_[1] ) =~ s/(.)\1{$max,}/$1 x $max/eg;
    return $new_string;
}