Add day 7

src/Day7.php

@@ -0,0 +1,65 @@
+<?php
+
+namespace AdventOfCode21;
+
+class Day7 extends AbstractCommand
+{
+    /**
+     * {@inheritdoc}
+     */
+    protected static int $day = 7;
+
+    /**
+     * {@inheritdoc}
+     */
+    protected function part1(array $data): int
+    {
+        return $this->calculateFuel($data[0], forPart2: false);
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    protected function part2(array $data): int
+    {
+        return $this->calculateFuel($data[0], forPart2: true);
+    }
+
+    /**
+     * @param string $data
+     * @param bool   $forPart2
+     *
+     * @return int
+     */
+    protected function calculateFuel(string $data, bool $forPart2 = false): int
+    {
+        $crabs = array_map(static fn (string $crab) => (int) $crab, explode(',', $data));
+        /** @psalm-param array{int: int} $fuelPerPosition */
+        $fuelPerPosition = [];
+
+        for ($position = min($crabs); $position <= max($crabs); ++$position) {
+            foreach ($crabs as $crab) {
+                if (!isset($fuelPerPosition[$position])) {
+                    $fuelPerPosition[$position] = 0;
+                }
+
+                $consumption = abs($position - $crab);
+
+                if ($forPart2) {
+                    $newConsumption = 0;
+                    // I'm sure there's another way than brute-forcing, but hey, this also works!
+                    for ($steps = 1; $steps <= $consumption; ++$steps) {
+                        $newConsumption += $steps;
+                    }
+
+                    $consumption = $newConsumption;
+                }
+
+                $fuelPerPosition[$position] += $consumption;
+            }
+        }
+
+        /** @psalm-suppress ArgumentTypeCoercion */
+        return min($fuelPerPosition);
+    }
+}