#!/usr/local/bin/perl
# day 2015-10

use strict;
use warnings;
use v5.32;

my $string = 1113122113;

#
# solution inspired by Abigail at:
# https://github.com/Abigail/AdventOfCode2015/blob/master/Day_10/look-and-say.pl
#

sub next_string {
    my $string = shift;
    my $result = "";

    while ( $string =~ /\G((.)\2*)/g) {

# the capture variable $1 represents what is matched in the outer most set of
# parentheses:  (.)\2*
# this matches for any number (.) followed by zero or more occurrences (*) of
# itself using a back reference (\2).
# the capture variable $2 represents the number.  The length of $1 represents
# the number of times that number was captured.  To see how it works, uncomment
# the following line:
#        say length $1, " ", $2, "s";
# the \G anchor can be used to start the next match on the same string where the
# last match left off.  For more information, please see:
# https://perldoc.perl.org/perlfaq6#What-good-is-%5CG-in-a-regular-expression?

        $result .= ( length $1 ) . $2;
    }

    return $result;
}

$string = next_string( $string ) foreach ( 1 .. 40 );
say "part 1: ", length $string;

$string = next_string( $string ) foreach ( 1 .. 10 ); # to reach 50 iterations
say "part 2: ", length $string;