From 25b46bc1158dcdf9c3cee8b64782ac05abe66c7a Mon Sep 17 00:00:00 2001
From: Timothy Warren <twarren@nabancard.com>
Date: Fri, 20 Dec 2024 10:42:01 -0500
Subject: [PATCH] Complete day 2 part 1

---
 2024/day2/index.php | 44 +++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 43 insertions(+), 1 deletion(-)

diff --git a/2024/day2/index.php b/2024/day2/index.php
index 5103afe..0b1a7d7 100644
--- a/2024/day2/index.php
+++ b/2024/day2/index.php
@@ -8,5 +8,47 @@ function parse_reports(): array
 	return array_map(fn (string $line) => explode(' ', $line), $lines);
 }
 
+class Report {
+	public function __construct(
+		public bool $allIncreasing,
+		public bool $allDecreasing,
+		public bool $safeDifference,
+	) {}
+
+	public function isSafe(): bool
+	{
+		return $this->safeDifference && ($this->allIncreasing || $this->allDecreasing);
+	}
+}
+
+function get_report_safety (array $report): Report {
+	$allIncreasing = true;
+	$allDecreasing = true;
+	$safeDifference = true;
+
+	$safeDiff = function ($curr, $prev): bool {
+		$diff = abs((int)$curr - (int)$prev);
+
+		return $diff > 0 && $diff <= 3;
+	};
+	$increasing = fn ($curr, $prev): bool => (int)$curr > (int)$prev;
+	$decreasing = fn ($curr, $prev): bool => (int)$curr < (int)$prev;
+
+	for ($i = 1;$i < count($report); $i++)
+	{
+		$curr = $report[$i];
+		$prev = $report[$i - 1];
+
+		$allIncreasing = $allIncreasing && $increasing($curr, $prev);
+		$allDecreasing = $allDecreasing && $decreasing($curr, $prev);
+		$safeDifference = $safeDifference && $safeDiff($curr, $prev);
+	}
+
+	return new Report($allIncreasing, $allDecreasing, $safeDifference);
+}
+
 $reports = parse_reports();
-print_r($reports);
\ No newline at end of file
+$reports = array_map('get_report_safety', $reports);
+$safeReports = count(array_filter($reports, fn (Report $r) => $r->isSafe()));
+
+echo "Number of safe reports: $safeReports\n";