Add day 1

src/Day1.php

@@ -0,0 +1,64 @@
+<?php
+
+namespace AdventOfCode21;
+
+use JetBrains\PhpStorm\ArrayShape;
+
+class Day1 extends AbstractCommand
+{
+    /**
+     * {@inheritdoc}
+     */
+    protected static int $day = 1;
+
+    /**
+     * {@inheritdoc}
+     */
+    protected function part1(array $data): int
+    {
+        $previous = null;
+        $increases = 0;
+
+        /** @var int $current */
+        foreach ($data as $current) {
+            if ($previous !== null && $previous < $current) {
+                ++$increases;
+            }
+
+            $previous = $current;
+        }
+
+        return $increases;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    protected function part2(array $data): int
+    {
+        $previousSum = null;
+        $increases = 0;
+
+        /**
+         * @var int $index
+         * @var int $indexValue
+         */
+        foreach ($data as $index => $indexValue) {
+            // If no 'next' indexes are available, skip.
+            if (!isset($data[$index + 1], $data[$index + 2])) {
+                continue;
+            }
+
+            // Calculate the sum of the current value and the next two.
+            $newSum = $indexValue + (int) $data[$index + 1] + (int) $data[$index + 2];
+
+            if ($previousSum !== null && $previousSum < $newSum) {
+                ++$increases;
+            }
+
+            $previousSum = $newSum;
+        }
+
+        return $increases;
+    }
+}