Add day 2

.gitignore

@@ -1,3 +1,4 @@
 /vendor/
 /.idea/
 /.php-cs-fixer.cache
+.DS_Store

aoc21

@@ -3,6 +3,7 @@
 require __DIR__.'/vendor/autoload.php';
 
 use AdventOfCode21\Day1;
+use AdventOfCode21\Day2;
 use AdventOfCode21\Puzzle;
 use Symfony\Component\Console\Application;
 
@@ -10,5 +11,6 @@ $application = new Application();
 
 $application->add(new Puzzle());
 $application->add(new Day1());
+$application->add(new Day2());
 
 $application->run();

data/day2/example.txt

@@ -0,0 +1,6 @@
+forward 5
+down 5
+forward 8
+up 3
+down 8
+forward 2

data/day2/puzzle.md

@@ -0,0 +1,67 @@
+# Day 2: Dive!
+
+[https://adventofcode.com/2021/day/2](https://adventofcode.com/2021/day/2)
+
+## Description
+
+### Part One
+
+Now, you need to figure out how to <span title="Tank, I need a pilot program for a B212 helicopter.">pilot this thing</span>.
+
+It seems like the submarine can take a series of commands like `forward 1`, `down 2`, or `up 3`:
+
+*   `forward X` increases the horizontal position by `X` units.
+*   `down X` _increases_ the depth by `X` units.
+*   `up X` _decreases_ the depth by `X` units.
+
+Note that since you're on a submarine, `down` and `up` affect your _depth_, and so they have the opposite result of what you might expect.
+
+The submarine seems to already have a planned course (your puzzle input). You should probably figure out where it's going. For example:
+
+    forward 5
+    down 5
+    forward 8
+    up 3
+    down 8
+    forward 2
+    
+
+Your horizontal position and depth both start at `0`. The steps above would then modify them as follows:
+
+*   `forward 5` adds `5` to your horizontal position, a total of `5`.
+*   `down 5` adds `5` to your depth, resulting in a value of `5`.
+*   `forward 8` adds `8` to your horizontal position, a total of `13`.
+*   `up 3` decreases your depth by `3`, resulting in a value of `2`.
+*   `down 8` adds `8` to your depth, resulting in a value of `10`.
+*   `forward 2` adds `2` to your horizontal position, a total of `15`.
+
+After following these instructions, you would have a horizontal position of `15` and a depth of `10`. (Multiplying these together produces _`150`_.)
+
+Calculate the horizontal position and depth you would have after following the planned course. _What do you get if you multiply your final horizontal position by your final depth?_
+
+### Part Two
+
+Based on your calculations, the planned course doesn't seem to make any sense. You find the submarine manual and discover that the process is actually slightly more complicated.
+
+In addition to horizontal position and depth, you'll also need to track a third value, _aim_, which also starts at `0`. The commands also mean something entirely different than you first thought:
+
+*   `down X` _increases_ your aim by `X` units.
+*   `up X` _decreases_ your aim by `X` units.
+*   `forward X` does two things:
+    *   It increases your horizontal position by `X` units.
+    *   It increases your depth by your aim _multiplied by_ `X`.
+
+Again note that since you're on a submarine, `down` and `up` do the opposite of what you might expect: "down" means aiming in the positive direction.
+
+Now, the above example does something different:
+
+*   `forward 5` adds `5` to your horizontal position, a total of `5`. Because your aim is `0`, your depth does not change.
+*   `down 5` adds `5` to your aim, resulting in a value of `5`.
+*   `forward 8` adds `8` to your horizontal position, a total of `13`. Because your aim is `5`, your depth increases by `8*5=40`.
+*   `up 3` decreases your aim by `3`, resulting in a value of `2`.
+*   `down 8` adds `8` to your aim, resulting in a value of `10`.
+*   `forward 2` adds `2` to your horizontal position, a total of `15`. Because your aim is `10`, your depth increases by `2*10=20` to a total of `60`.
+
+After following these new instructions, you would have a horizontal position of `15` and a depth of `60`. (Multiplying these produces _`900`_.)
+
+Using this new interpretation of the commands, calculate the horizontal position and depth you would have after following the planned course. _What do you get if you multiply your final horizontal position by your final depth?_

src/Day2.php

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+<?php
+
+namespace AdventOfCode21;
+
+class Day2 extends AbstractCommand
+{
+    /**
+     * {@inheritdoc}
+     */
+    protected static int $day = 2;
+
+    /**
+     * {@inheritdoc}
+     */
+    protected function part1(array $data): int
+    {
+        $depth = 0;
+        $horizontal = 0;
+
+        /** @var string $current */
+        foreach ($data as $current) {
+            /**
+             * @var string $direction
+             * @var int    $distance
+             */
+            [$direction, $distance] = explode(' ', $current);
+
+            switch ($direction) {
+                case 'forward':
+                    $horizontal += $distance;
+
+                    break;
+
+                case 'down':
+                    $depth += $distance;
+
+                    break;
+
+                case 'up':
+                    $depth -= $distance;
+
+                    break;
+            }
+        }
+
+        return $depth * $horizontal;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    protected function part2(array $data): int
+    {
+        $aim = 0;
+        $depth = 0;
+        $horizontal = 0;
+
+        /** @var string $current */
+        foreach ($data as $current) {
+            /**
+             * @var string $direction
+             * @var int    $distance
+             */
+            [$direction, $distance] = explode(' ', $current);
+
+            switch ($direction) {
+                case 'forward':
+                    $horizontal += $distance;
+                    $depth += $distance * $aim;
+
+                    break;
+
+                case 'down':
+                    $aim += $distance;
+
+                    break;
+
+                case 'up':
+                    $aim -= $distance;
+
+                    break;
+            }
+        }
+
+        return $horizontal * $depth;
+    }
+}

tests/Day2Test.php

@@ -0,0 +1,24 @@
+<?php
+
+namespace Tests;
+
+use AdventOfCode21\Day2;
+
+/**
+ * @internal
+ */
+class Day2Test extends AbstractTestCase
+{
+    public static int $part1ExampleResult = 150;
+    public static int $part1Result = 1654760;
+
+    public static int $part2ExampleResult = 900;
+    public static int $part2Result = 1956047400;
+
+    public function setupDay(): Day2
+    {
+        return new class() extends Day2 {
+            use ReturnTestableResults;
+        };
+    }
+}