Add day 7.

day07.pl

@@ -0,0 +1,60 @@
+#!/usr/bin/env perl
+
+use strict;
+use warnings;
+
+
+my @results = ();
+my @expressions = ();
+while (<>) {
+	next if !/(\d+): ((?:\d+ ?)+)/;
+	push @results, $1;
+
+	my @numbers = split ' ', $2;
+	push @expressions, \@numbers;
+}
+
+my $answer = 0;
+for my $i (0 .. $#results) {
+	print "$i/$#results\n";
+	my $result = $results[$i];
+	my $expression = $expressions[$i];
+
+	my @operators = map { 0 } 0..($#$expression - 1);
+	while (1) {
+		my $total = $expression->[0];
+		for my $i (0 .. $#operators) {
+			my $operator = $operators[$i];
+			my $number = $expression->[$i + 1];
+			if ($operator == 0) {
+				$total += $number;
+			} elsif ($operator == 1) {
+				$total *= $number;
+			} elsif ($operator == 2) {
+				$total .= $number;
+			}
+		}
+
+		if ($total == $result) {
+			$answer += $result;
+			last;
+		}
+
+		my $done = 0;
+		$operators[0]++;
+		for $i (0 .. $#operators) {
+			my $operator = $operators[$i];
+			if ($operator == 3) {
+				if (!defined($operators[$i + 1])) {
+					$done = 1;
+					last;
+				}
+				$operators[$i] = 0;
+				$operators[$i + 1]++;
+			}
+		}
+		last if $done;
+	}
+}
+
+print "$answer\n";