Year 2015

[aoc.git] / 2015 / 25.pl

diff --git a/2015/25.pl b/2015/25.pl
new file mode 100755 (executable)
index 0000000..b5a6e70
--- /dev/null
+++ b/2015/25.pl
@@ -0,0 +1,43 @@
+#!/usr/bin/perl -w
+
+use v5.16;
+use strict;
+
+my %rules;
+my %persons;
+
+while (<>) {
+       my ($p1, $sign, $score, $p2) = /(\w+) would (\w+) (\d+) happiness units? by sitting next to (\w+)\./;
+       $sign = ($sign eq 'gain') ? 1 : -1;
+       $rules{$p1}{$p2} = $sign * $score;
+       $persons{$p1}++;
+       $persons{$p2}++;
+}
+
+my $max;
+sub perm {
+       my ($done, $rest) = @_;
+
+       if (@$rest) {
+               for my $i (0 .. $#$rest) {
+                       my @nd = @$done;
+                       my @nr = @$rest;
+                       push @nd, splice @nr, $i, 1;
+                       perm(\@nd, \@nr);
+               }
+       } else {
+               my $score;
+               for my $i (0 .. $#$done) {
+                       my $self = $done->[$i];
+                       my @neigh = ($done->[$i-1], $done->[$i == $#$done ? 0 : $i+1]);
+                       for my $n (@neigh) {
+                               $score += $rules{$self}{$n};
+                       }
+               }
+               $max = $score if !defined $max || $max < $score;        
+       }
+}
+
+perm([], [ keys %persons ]);
+say $max;
+