Complete day 2.

.gitignore

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+*.txt

day02.pl

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+#!/usr/bin/env perl
+
+use strict;
+use warnings;
+
+use List::Util qw(reduce);
+
+my @reports;
+while (<>) {
+	my @numbers = split;
+	next unless @numbers;
+	push @reports, \@numbers;
+}
+
+print "Part 1:\n";
+my $safe_reports = reduce { $a + $b } map { is_safe(@$_) } @reports;
+print $safe_reports . "\n";
+
+print "Part 2:\n";
+$safe_reports = reduce { $a + $b } map { is_safe_with_modification(@$_) } @reports;
+print $safe_reports . "\n";
+
+sub is_safe {
+	return (is_increasing(@_) || is_decreasing(@_)) && max_diff(@_);
+}
+
+sub is_safe_with_modification {
+	return 1 if is_safe(@_);
+
+	# This is really dumb...
+	for (my $i = 0; $i < @_; $i++) {
+		my @to_test = @_;
+		splice @to_test, $i, 1;
+		return 1 if is_safe(@to_test);
+	}
+
+	return 0;
+}
+
+sub is_increasing {
+	my $prev = shift;
+	for (@_) {
+		return 0 if ($_ <= $prev);
+		$prev = $_;
+	}
+	return 1;
+}
+
+sub is_decreasing {
+	my $prev = shift;
+	for (@_) {
+		return 0 if ($_ >= $prev);
+		$prev = $_;
+	}
+	return 1;
+}
+
+sub max_diff {
+	my $prev = shift;
+
+	for (@_) {
+		if ((abs($_ - $prev) > 3) || (abs($_ - $prev) < 1)) {
+			return 0;
+		}
+		$prev = $_;
+	}
+	return 1;
+}