aoc_2021_day12_min.pl

#!/usr/bin/perl

use strict;

my %map=();

while( my $line = <STDIN> ) {
        chomp( $line );
        my ( $f, $t ) = split( /-/, $line );
        push( @{$map{$f}}, $t ) if( $t ne "start" );
        push( @{$map{$t}}, $f ) if( $f ne "start" );
}

my $routes=0;

foreach my $poss ( @{$map{'start'}} ) {
        my %visited=(); go( $poss, \%visited, 1 );
}

print "part1: $routes\n";

$routes=0;

foreach my $poss ( @{$map{'start'}} ) {
        my %visited=(); go( $poss, \%visited, 0 );
}

print "part2: $routes\n";

exit;

sub go {
        my ( $where, $v, $vtwice ) = @_;
        $v->{$where}++ if( $where eq lc($where) );
        foreach my $poss ( @{$map{$where}} ) {
                if( $poss eq "end" ) { $routes++; next; }
                next if( exists( $v->{$poss} ) && $vtwice );
                my %visited=%$v;
                go( $poss, \%visited, exists( $v->{$poss} ) ? 1 : $vtwice );
        }
}