Moved 2020 to a subdir

[aoc.git] / 2020 / 16.pl

diff --git a/2020/16.pl b/2020/16.pl
new file mode 100755 (executable)
index 0000000..899e942
--- /dev/null
+++ b/2020/16.pl
@@ -0,0 +1,40 @@
+#!/usr/bin/perl -w
+
+use strict;
+
+my @code = map { [ split /\s+/ ] } <>;
+
+for my $i (0 .. $#code) {
+       if ($code[$i]->[0] eq 'nop') {
+               local $code[$i]->[0] = 'jmp';
+               interp(\@code);
+       } elsif ($code[$i]->[0] eq 'jmp') {
+               local $code[$i]->[0] = 'nop';
+               interp(\@code);
+       }
+}
+               
+sub interp {
+       my ($code) = @_;
+       my $acc = 0;
+       my $pc = 0;
+       my %seen;
+
+       while (!$seen{$pc} && $pc != @$code) {
+               $seen{$pc} = 1;
+               my ($ins, $arg) = @{ $code->[$pc] };
+               # print "pc=$pc, acc=$acc, $ins $arg\n";
+               if ($ins eq 'nop') {
+                       $pc++;
+               } elsif ($ins eq 'acc') {
+                       $acc += $arg; $pc++;
+               } elsif ($ins eq 'jmp') {
+                       $pc += $arg;
+               }
+       }
+       if ($pc == @$code) {
+               print "terminating with acc=$acc.\n";
+               exit 0;
+       }
+       # print "\n";
+}