1 files changed, 96 insertions, 0 deletions
diff --git a/6.pl b/6.pl
new file mode 100644
index 0000000..6705a67
--- /dev/null
+++ b/6.pl
@@ -0,0 +1,96 @@
+#!/usr/bin/env perl
+use strict;
+use warnings;
+
+my @original_grid;
+my @grid;
+my @pos = (0,0);
+my @start_pos = (0,0);
+my %seen_positions;
+
+open(my $fh, "6-input.txt") or die;
+while (<$fh>) { chomp; push @original_grid, [split //]; }
+close($fh);
+
+@grid = map { [@$_] } @original_grid;
+for (my $i=0; $i<scalar @grid; $i++) {
+  for (my $j=0; $j<scalar @{$grid[$i]}; $j++) {
+    if ($grid[$i][$j] eq '^') {
+      $start_pos[0] = $i;
+      $start_pos[1] = $j;
+    }
+  }
+}
+
+$pos[0] = $start_pos[0];
+$pos[1] = $start_pos[1];
+
+sub tick {
+  my ($position, $grid) = @_;
+  my $direction = $grid[$pos[0]][$pos[1]];
+  if ($direction eq '^') {
+      if ($pos[0]-1 < 0) { $grid[$pos[0]][$pos[1]] = 'X'; }
+      elsif ($pos[0]-1 >= 0 and ($grid[$pos[0]-1][$pos[1]] eq '.' or $grid[$pos[0]-1][$pos[1]] eq 'X')) {
+        $grid[$pos[0]][$pos[1]] = 'X';
+        $pos[0]--;
+        $grid[$pos[0]][$pos[1]] = '^';
+      }
+      else { $grid[$pos[0]][$pos[1]] = '>'; }
+  } elsif ($direction eq '>') {
+    if ($pos[1]+1 >= scalar @{$grid[$pos[0]]}) { $grid[$pos[0]][$pos[1]] = 'X'; }
+    elsif ($pos[1]+1 < scalar @{$grid[$pos[0]]} and ($grid[$pos[0]][$pos[1]+1] eq '.' or $grid[$pos[0]][$pos[1]+1] eq 'X')) {
+      $grid[$pos[0]][$pos[1]] = 'X';
+      $pos[1]++;
+      $grid[$pos[0]][$pos[1]] = '>';
+    }
+    else { $grid[$pos[0]][$pos[1]] = 'V'; }
+  } elsif ($direction eq 'V') {
+    if ($pos[0]+1 >= scalar @grid) { $grid[$pos[0]][$pos[1]] = 'X'; }
+    elsif ($pos[0]+1 < scalar @grid and ($grid[$pos[0]+1][$pos[1]] eq '.' or $grid[$pos[0]+1][$pos[1]] eq 'X')) {
+      $grid[$pos[0]][$pos[1]] = 'X';
+      $pos[0]++;
+      $grid[$pos[0]][$pos[1]] = 'V';
+    }
+    else { $grid[$pos[0]][$pos[1]] = '<'; }
+  } elsif ($direction eq '<') {
+    if ($pos[1]-1 < 0) { $grid[$pos[0]][$pos[1]] = 'X'; }
+    elsif ($pos[1]-1 >= 0 and ($grid[$pos[0]][$pos[1]-1] eq '.' or $grid[$pos[0]][$pos[1]-1] eq 'X')) {
+      $grid[$pos[0]][$pos[1]] = 'X';
+      $pos[1]--;
+      $grid[$pos[0]][$pos[1]] = '<';
+    }
+    else { $grid[$pos[0]][$pos[1]] = '^'; }
+  } else { return 0; }
+  return 1;
+}
+
+while (tick(\@pos, \@grid)) { $seen_positions{"$pos[0],$pos[1]"} = 1; }
+my $pone = 0;
+foreach(@grid) { foreach (@$_) { $pone++ if $_ eq 'X'; } }
+print "puzzle 1: ", $pone, "\n";
+
+my $loops = 0;
+for (my $i=0; $i<scalar @original_grid; $i++) {
+  for (my $j=0; $j<scalar @{$original_grid[$i]}; $j++) {
+    if ($original_grid[$i][$j] eq '.' and defined $seen_positions{"$i,$j"}) {
+      @grid = map { [@$_] } @original_grid;
+      $pos[0] = $start_pos[0];
+      $pos[1] = $start_pos[1];
+      $grid[$i][$j] = 'O';
+      my %seen_position;
+      LOOP: while (tick(\@pos, \@grid)) {
+        my $direction = $grid[$pos[0]][$pos[1]];
+        if (not defined $seen_position{"$pos[0],$pos[1]"}) {
+            $seen_position{"$pos[0],$pos[1]"} = [$direction];
+            next;
+        }
+        foreach (@{ $seen_position{"$pos[0],$pos[1]"} }) {
+          if ($_ eq $direction) { $loops++; last LOOP; }
+        }
+        push @{ $seen_position{"$pos[0],$pos[1]"} }, $direction;
+      }
+    }
+  }
+}
+
+print "puzzle 2: ", $loops, "\n";