Add Rotational Cipher Exercise (#635)

Author: tomasnorre

config.json

@@ -1195,6 +1195,14 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 3
+      },
+      {
+        "slug": "rotational-cipher",
+        "name": "Rotational Cipher",
+        "uuid": "61add6ab-9eaa-4fbc-b060-8ac44f47fad7",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 3
       }
     ]
   },

exercises/practice/rotational-cipher/.docs/instructions.append.md

@@ -0,0 +1,3 @@
+~~~~exercism/note
+Do not use PHP functions like `str_rot13()` to solve this exercise! Only use basic string and character manipulation functions.
+~~~~

exercises/practice/rotational-cipher/.docs/instructions.md

@@ -0,0 +1,29 @@
+# Instructions
+
+Create an implementation of the rotational cipher, also sometimes called the Caesar cipher.
+
+The Caesar cipher is a simple shift cipher that relies on transposing all the letters in the alphabet using an integer key between `0` and `26`.
+Using a key of `0` or `26` will always yield the same output due to modular arithmetic.
+The letter is shifted for as many values as the value of the key.
+
+The general notation for rotational ciphers is `ROT + <key>`.
+The most commonly used rotational cipher is `ROT13`.
+
+A `ROT13` on the Latin alphabet would be as follows:
+
+```text
+Plain:  abcdefghijklmnopqrstuvwxyz
+Cipher: nopqrstuvwxyzabcdefghijklm
+```
+
+It is stronger than the Atbash cipher because it has 27 possible keys, and 25 usable keys.
+
+Ciphertext is written out in the same formatting as the input including spaces and punctuation.
+
+## Examples
+
+- ROT5 `omg` gives `trl`
+- ROT0 `c` gives `c`
+- ROT26 `Cool` gives `Cool`
+- ROT13 `The quick brown fox jumps over the lazy dog.` gives `Gur dhvpx oebja sbk whzcf bire gur ynml qbt.`
+- ROT13 `Gur dhvpx oebja sbk whzcf bire gur ynml qbt.` gives `The quick brown fox jumps over the lazy dog.`

exercises/practice/rotational-cipher/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "tomasnorre"
+  ],
+  "files": {
+    "solution": [
+      "RotationalCipher.php"
+    ],
+    "test": [
+      "RotationalCipherTest.php"
+    ],
+    "example": [
+      ".meta/example.php"
+    ]
+  },
+  "blurb": "Create an implementation of the rotational cipher, also sometimes called the Caesar cipher.",
+  "source": "Wikipedia",
+  "source_url": "https://en.wikipedia.org/wiki/Caesar_cipher"
+}

exercises/practice/rotational-cipher/.meta/example.php

@@ -0,0 +1,22 @@
+<?php
+
+declare(strict_types=1);
+
+class RotationalCipher
+{
+    public function rotate(string $text, int $shift): string
+    {
+        return implode('', array_map(static function ($c) use ($shift) {
+            $isUpper = preg_match('/[A-Z]/', $c);
+            $isAlpha = preg_match('/[a-z]/i', $c);
+            $charShift = $isUpper ? ord('A') : ord('a');
+
+            if ($isAlpha) {
+                $shiftedCharCode = (ord($c) - $charShift + $shift) % 26 + $charShift;
+                return chr($shiftedCharCode);
+            }
+
+            return $c;
+        }, str_split($text)));
+    }
+}

exercises/practice/rotational-cipher/.meta/tests.toml

@@ -0,0 +1,40 @@
+# This is an auto-generated file.
+#
+# Regenerating this file via `configlet sync` will:
+# - Recreate every `description` key/value pair
+# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
+# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
+# - Preserve any other key/value pair
+#
+# As user-added comments (using the # character) will be removed when this file
+# is regenerated, comments can be added via a `comment` key.
+
+[74e58a38-e484-43f1-9466-877a7515e10f]
+description = "rotate a by 0, same output as input"
+
+[7ee352c6-e6b0-4930-b903-d09943ecb8f5]
+description = "rotate a by 1"
+
+[edf0a733-4231-4594-a5ee-46a4009ad764]
+description = "rotate a by 26, same output as input"
+
+[e3e82cb9-2a5b-403f-9931-e43213879300]
+description = "rotate m by 13"
+
+[19f9eb78-e2ad-4da4-8fe3-9291d47c1709]
+description = "rotate n by 13 with wrap around alphabet"
+
+[a116aef4-225b-4da9-884f-e8023ca6408a]
+description = "rotate capital letters"
+
+[71b541bb-819c-4dc6-a9c3-132ef9bb737b]
+description = "rotate spaces"
+
+[ef32601d-e9ef-4b29-b2b5-8971392282e6]
+description = "rotate numbers"
+
+[32dd74f6-db2b-41a6-b02c-82eb4f93e549]
+description = "rotate punctuation"
+
+[9fb93fe6-42b0-46e6-9ec1-0bf0a062d8c9]
+description = "rotate all letters"

exercises/practice/rotational-cipher/RotationalCipher.php

@@ -0,0 +1,33 @@
+<?php
+
+/*
+ * By adding type hints and enabling strict type checking, code can become
+ * easier to read, self-documenting and reduce the number of potential bugs.
+ * By default, type declarations are non-strict, which means they will attempt
+ * to change the original type to match the type specified by the
+ * type-declaration.
+ *
+ * In other words, if you pass a string to a function requiring a float,
+ * it will attempt to convert the string value to a float.
+ *
+ * To enable strict mode, a single declare directive must be placed at the top
+ * of the file.
+ * This means that the strictness of typing is configured on a per-file basis.
+ * This directive not only affects the type declarations of parameters, but also
+ * a function's return type.
+ *
+ * For more info review the Concept on strict type checking in the PHP track
+ * <link>.
+ *
+ * To disable strict typing, comment out the directive below.
+ */
+
+declare(strict_types=1);
+
+class RotationalCipher
+{
+    public function rotate(string $text, int $shift): string
+    {
+        throw new \BadMethodCallException(sprintf('Implement the %s method', __FUNCTION__));
+    }
+}

exercises/practice/rotational-cipher/RotationalCipherTest.php

@@ -0,0 +1,118 @@
+<?php
+
+declare(strict_types=1);
+
+class RotationalCipherTest extends PHPUnit\Framework\TestCase
+{
+    private RotationalCipher $rotationalCipher;
+
+    public static function setUpBeforeClass(): void
+    {
+        require_once 'RotationalCipher.php';
+    }
+
+    protected function setUp(): void
+    {
+        $this->rotationalCipher = new RotationalCipher();
+    }
+
+    /**
+     * uuid: 74e58a38-e484-43f1-9466-877a7515e10f
+     */
+    public function testRotateAByZero(): void
+    {
+        $expected = 'a';
+        $actual = $this->rotationalCipher->rotate('a', 0);
+        $this->assertEquals($expected, $actual);
+    }
+
+    /**
+     * uuid: 7ee352c6-e6b0-4930-b903-d09943ecb8f5
+     */
+    public function testRotateAByOne(): void
+    {
+        $expected = 'b';
+        $actual = $this->rotationalCipher->rotate('a', 1);
+        $this->assertEquals($expected, $actual);
+    }
+
+    /**
+     * uuid: edf0a733-4231-4594-a5ee-46a4009ad764
+     */
+    public function testRotateABy26(): void
+    {
+        $expected = 'a';
+        $actual = $this->rotationalCipher->rotate('a', 26);
+        $this->assertEquals($expected, $actual);
+    }
+
+    /**
+     * uuid: e3e82cb9-2a5b-403f-9931-e43213879300
+     */
+    public function testRotateMBy13(): void
+    {
+        $expected = 'z';
+        $actual = $this->rotationalCipher->rotate('m', 13);
+        $this->assertEquals($expected, $actual);
+    }
+
+    /**
+     * uuid: 19f9eb78-e2ad-4da4-8fe3-9291d47c1709
+     */
+    public function testRotateNBy13WithWrapAroundAlphabet(): void
+    {
+        $expected = 'a';
+        $actual = $this->rotationalCipher->rotate('n', 13);
+        $this->assertEquals($expected, $actual);
+    }
+
+    /**
+     * uuid: a116aef4-225b-4da9-884f-e8023ca6408a
+     */
+    public function testRotateCapitalLetters(): void
+    {
+        $expected = 'TRL';
+        $actual = $this->rotationalCipher->rotate('OMG', 5);
+        $this->assertEquals($expected, $actual);
+    }
+
+    /**
+     * uuid: 71b541bb-819c-4dc6-a9c3-132ef9bb737b
+     */
+    public function testRotateSpaces(): void
+    {
+        $expected = 'T R L';
+        $actual = $this->rotationalCipher->rotate('O M G', 5);
+        $this->assertEquals($expected, $actual);
+    }
+
+    /**
+     * uuid: ef32601d-e9ef-4b29-b2b5-8971392282e6
+     */
+    public function testRotateNumbers(): void
+    {
+        $expected = 'Xiwxmrk 1 2 3 xiwxmrk';
+        $actual = $this->rotationalCipher->rotate('Testing 1 2 3 testing', 4);
+        $this->assertEquals($expected, $actual);
+    }
+
+    /**
+     * uuid: 32dd74f6-db2b-41a6-b02c-82eb4f93e549
+     */
+    public function testRotatePunctuation(): void
+    {
+        $expected = "Gzo'n zvo, Bmviyhv!";
+        $actual = $this->rotationalCipher->rotate("Let's eat, Grandma!", 21);
+        $this->assertEquals($expected, $actual);
+    }
+
+    /**
+     * uuid: 9fb93fe6-42b0-46e6-9ec1-0bf0a062d8c9
+     */
+    public function testRotateAllLetters(): void
+    {
+        $expected = 'Gur dhvpx oebja sbk whzcf bire gur ynml qbt.';
+        $actual = $this->rotationalCipher->rotate('The quick brown fox jumps over the lazy dog.', 13);
+        $this->assertEquals($expected, $actual);
+    }
+}