Day 10 part 1 & 2

2015/day-10.php

@@ -0,0 +1,45 @@
+<?php
+
+ini_set("memory_limit", "-1");
+
+require __DIR__ . '/../vendor/autoload.php';
+
+use adventofcode\Year2015\LookAndSay;
+
+/**
+ * --- Day 10: Elves Look, Elves Say ---
+ *
+ * Today, the Elves are playing a game called look-and-say. They take turns making sequences by reading aloud the
+ * previous sequence and using that reading as the next sequence. For example, 211 is read as "one two, two ones",
+ * which becomes 1221 (1 2, 2 1s).
+ *
+ * Look-and-say sequences are generated iteratively, using the previous value as input for the next step. For each
+ * step, take the previous value, and replace each run of digits (like 111) with the number of digits (3) followed
+ * by the digit itself (1).
+ *
+ * For example:
+ *
+ *   - 1 becomes 11 (1 copy of digit 1).
+ *   - 11 becomes 21 (2 copies of digit 1).
+ *   - 21 becomes 1211 (one 2 followed by one 1).
+ *   - 1211 becomes 111221 (one 1, one 2, and two 1s).
+ *   - 111221 becomes 312211 (three 1s, two 2s, and one 1).
+ *
+ * Starting with the digits in your puzzle input, apply this process 40 times. What is the length of the result?
+ */
+
+$lookAndSay = new LookAndSay();
+$result = $lookAndSay->play('3113322113', 40);
+print("The length of the result after 40 rounds is " . strlen($result) . ".\n");
+
+/**
+ * Neat, right? You might also enjoy hearing John Conway talking about this sequence (that's Conway of Conway's
+ * Game of Life fame).
+ *
+ * Now, starting again with the digits in your puzzle input, apply this process 50 times. What is the length of
+ * the new result?
+ */
+
+$lookAndSay = new LookAndSay();
+$result = $lookAndSay->play('3113322113', 50);
+print("The length of the result after 50 rounds is " . strlen($result) . ".\n");

2015/src/LookAndSay.php

@@ -0,0 +1,54 @@
+<?php
+
+namespace adventofcode\Year2015;
+
+class LookAndSay
+{
+    /**
+     * Play a game of Look and Say.
+     *
+     * @param  string $input
+     * @param  int    $rounds Number of rounds to play
+     * @return string
+     */
+    public function play(string $input, int $rounds): string
+    {
+        $finalResult = $input;
+
+        for ($i = 0; $i < $rounds; $i++) {
+            $characters = str_split($finalResult);
+
+            if (count($characters) === 1) {
+                $finalResult = '1' . $characters[0];
+                continue;
+            }
+
+            $previousCharacter = $characters[0];
+            $characterCount = 0;
+            $roundResult = '';
+
+            foreach ($characters as $index => $character) {
+                if ($character === $previousCharacter) {
+                    $characterCount++;
+
+                    if ($index === count($characters) - 1) {
+                        $roundResult .= $characterCount . $previousCharacter;
+                    }
+                    continue;
+                }
+
+                $roundResult .= $characterCount . $previousCharacter;
+                $previousCharacter = $character;
+                $characterCount = 1;
+
+                if ($index === count($characters) - 1) {
+                    $roundResult .= $characterCount . $previousCharacter;
+                }
+            }
+
+            $finalResult = $roundResult;
+        }
+
+        return $finalResult;
+    }
+}

2015/src/NiceString.php

@@ -4,8 +4,8 @@
 
 class NiceString
 {
-    const MODE_V1 = 'v1';
-    const MODE_V2 = 'v2';
+    public const MODE_V1 = 'v1';
+    public const MODE_V2 = 'v2';
 
     /**
      * Determines if the input contains a naughty string.
@@ -104,8 +104,10 @@ public function isNice(string $input, string $mode = self::MODE_V1): bool
     {
         switch ($mode) {
             case self::MODE_V2:
-                if ($this->containsMultipleLetterPairs($input) &&
-                    $this->containsDuplicateLetterWithOneCharacterBetween($input)) {
+                if (
+                    $this->containsMultipleLetterPairs($input) &&
+                    $this->containsDuplicateLetterWithOneCharacterBetween($input)
+                ) {
                     return true;
                 }
 

2015/tests/LookAndSayTest.php

@@ -0,0 +1,34 @@
+<?php
+
+namespace adventofcode\Year2015\Test;
+
+use adventofcode\Year2015\LookAndSay;
+use PHPUnit\Framework\TestCase;
+
+class LookAndSayTest extends TestCase
+{
+    protected $lookAndSay;
+
+    protected function setup(): void
+    {
+        $this->lookAndSay = new LookAndSay();
+    }
+
+    public function testPlay()
+    {
+        ini_set("memory_limit", "-1");
+
+        // Day 10 Part 1 example input
+        $result = $this->lookAndSay->play('1', 5);
+        $this->assertEquals('312211', $result);
+        $this->assertEquals(6, strlen($result));
+
+        // Day 10 Part 1 actual input
+        $result = $this->lookAndSay->play('3113322113', 40);
+        $this->assertEquals(329356, strlen($result));
+
+        // Day 10 Part 2 actual input
+        $result = $this->lookAndSay->play('3113322113', 50);
+        $this->assertEquals(4666278, strlen($result));
+    }
+}

README.md

@@ -20,7 +20,7 @@ of changes and trends in that community.
 | Day 07 |               |               |               |               |               |               |               |      |               |
 | Day 08 |               |               |               |               |               |               |               |      |               |
 | Day 09 |               |               |               |               |               |               |               |      |               |
-| Day 10 |               |               |               |               |               |               |               |      |               |
+| Day 10 |               |               |               |               |               |               |               |      | :star: :star: |
 | Day 11 |               |               |               |               |               |               |               |      |               |
 | Day 12 |               |               |               |               |               |               |               |      |               |
 | Day 13 |               |               |               |               |               |               |               |      |               |