aoc_2021_day11.pl

#!/usr/bin/perl

use strict;

my $y=0;
my %map=();

while( my $line = <STDIN> ) {
        chomp( $line );
        my $x=0;
        foreach my $o ( split( //, $line ) ) {
                $map{$x.":".$y}=$o;
                $x++;
        }
        $y++;
}

my $part1=0;

my $step=0;
while( 1 ) {
        $step++;
        foreach my $k ( keys %map ) { incr($k); }
        my $nosflash=0;
        foreach my $k ( keys %map ) {
                if( $map{$k} eq "*" ) {
                        $nosflash++;
                        $map{$k}=0;
                }
        }
        if( $step == 100 ) { print "part1: $part1\n"; }
        if( $nosflash == 100 ) { print "part2: $step\n"; last; }
}

exit;

sub incr {
        my ( $k ) = @_;
        if( $map{$k} ne "*" ) {
                $map{$k}++;
                if( $map{$k} > 9 ) {
                        $map{$k}="*";
                        flash($k);
                }
        }
}

sub flash {
        my ( $k ) = @_;
        my ( $fx, $fy ) = split( /:/, $k );
        $part1++;
        for my $dx ( -1..1 ) {
                for my $dy ( -1..1 ) {
                        next if( $dx == 0 && $dy == 0 );
                        my $dk=($fx+$dx).":".($fy+$dy);
                        incr( $dk ) if( exists( $map{$dk} ) );
                }
        }
}