Add rotational-cipher exercise (#690)

config.json

@@ -785,6 +785,14 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 2
+      },
+      {
+        "slug": "rotational-cipher",
+        "name": "Rotational Cipher",
+        "uuid": "dbc46c87-97d4-4739-ad31-e9fbc2ec7c1e",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 3
       }
     ]
   },

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 +1,22 @@
+{
+  "authors": [
+    "glennj"
+  ],
+  "contributors": [
+    "m-dango"
+  ],
+  "files": {
+    "solution": [
+      "lib/RotationalCipher.pm"
+    ],
+    "test": [
+      "t/rotational-cipher.t"
+    ],
+    "example": [
+      ".meta/solutions/lib/RotationalCipher.pm"
+    ]
+  },
+  "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/solutions/lib/RotationalCipher.pm

@@ -0,0 +1,25 @@
+package RotationalCipher;
+
+use strict;
+use warnings;
+use experimental qw<signatures postderef postderef_qq>;
+
+use Exporter qw<import>;
+our @EXPORT_OK = qw<caesar_cipher>;
+
+# from https://perldoc.pl/perlop#tr/SEARCHLIST/REPLACEMENTLIST/cdsr
+# > Because the transliteration table is built at compile time, neither the
+# > SEARCHLIST nor the REPLACEMENTLIST are subjected to double quote
+# > interpolation. That means that if you want to use variables, you must
+# > use an eval()
+
+sub caesar_cipher ( $text, $shift ) {
+    my $alpha = 'abcdefghijklmnopqrstuvwxyz';
+    my $rotated = substr( $alpha, $shift % 26 ) . substr( $alpha, 0, $shift % 26 );
+    $alpha   .= uc $alpha;
+    $rotated .= uc $rotated;
+
+    return eval "\$text =~ tr/$alpha/$rotated/r";
+}
+
+1;

exercises/practice/rotational-cipher/.meta/solutions/t/rotational-cipher.t

@@ -0,0 +1 @@
+../../../t/rotational-cipher.t

exercises/practice/rotational-cipher/.meta/template-data.yaml

@@ -0,0 +1,33 @@
+subs: caesar_cipher
+properties:
+  rotate:
+    test: |-
+      use Data::Dmp;
+      sprintf(<<'END', dmp($case->{input}{text}), $case->{input}{shiftKey}, dmp($case->{expected}), dmp($case->{description}));
+      is(
+        caesar_cipher(%s, %s),
+        %s,
+        %s
+      );
+      END
+
+stub: |-
+  sub caesar_cipher ($text, $shift_key) {
+    return undef;
+  }
+
+example: |-
+  # from https://perldoc.pl/perlop#tr/SEARCHLIST/REPLACEMENTLIST/cdsr
+  # > Because the transliteration table is built at compile time, neither the
+  # > SEARCHLIST nor the REPLACEMENTLIST are subjected to double quote
+  # > interpolation. That means that if you want to use variables, you must
+  # > use an eval()
+
+  sub caesar_cipher ($text, $shift) {
+    my $alpha = 'abcdefghijklmnopqrstuvwxyz';
+    my $rotated = substr($alpha, $shift % 26) . substr($alpha, 0, $shift % 26);
+    $alpha .= uc $alpha;
+    $rotated .= uc $rotated;
+
+    return eval "\$text =~ tr/$alpha/$rotated/r";
+  }

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/lib/RotationalCipher.pm

@@ -0,0 +1,12 @@
+package RotationalCipher;
+
+use v5.40;
+
+use Exporter qw<import>;
+our @EXPORT_OK = qw<caesar_cipher>;
+
+sub caesar_cipher ( $text, $shift_key ) {
+    return undef;
+}
+
+1;

exercises/practice/rotational-cipher/t/rotational-cipher.t

@@ -0,0 +1,69 @@
+#!/usr/bin/env perl
+use Test2::V0;
+
+use FindBin qw<$Bin>;
+use lib "$Bin/../lib", "$Bin/../local/lib/perl5";
+
+use RotationalCipher qw<caesar_cipher>;
+
+is( # begin: 74e58a38-e484-43f1-9466-877a7515e10f
+    caesar_cipher( "a", 0 ),
+    "a",
+    "rotate a by 0, same output as input"
+); # end: 74e58a38-e484-43f1-9466-877a7515e10f
+
+is( # begin: 7ee352c6-e6b0-4930-b903-d09943ecb8f5
+    caesar_cipher( "a", 1 ),
+    "b",
+    "rotate a by 1"
+); # end: 7ee352c6-e6b0-4930-b903-d09943ecb8f5
+
+is( # begin: edf0a733-4231-4594-a5ee-46a4009ad764
+    caesar_cipher( "a", 26 ),
+    "a",
+    "rotate a by 26, same output as input"
+); # end: edf0a733-4231-4594-a5ee-46a4009ad764
+
+is( # begin: e3e82cb9-2a5b-403f-9931-e43213879300
+    caesar_cipher( "m", 13 ),
+    "z",
+    "rotate m by 13"
+); # end: e3e82cb9-2a5b-403f-9931-e43213879300
+
+is( # begin: 19f9eb78-e2ad-4da4-8fe3-9291d47c1709
+    caesar_cipher( "n", 13 ),
+    "a",
+    "rotate n by 13 with wrap around alphabet"
+); # end: 19f9eb78-e2ad-4da4-8fe3-9291d47c1709
+
+is( # begin: a116aef4-225b-4da9-884f-e8023ca6408a
+    caesar_cipher( "OMG", 5 ),
+    "TRL",
+    "rotate capital letters"
+); # end: a116aef4-225b-4da9-884f-e8023ca6408a
+
+is( # begin: 71b541bb-819c-4dc6-a9c3-132ef9bb737b
+    caesar_cipher( "O M G", 5 ),
+    "T R L",
+    "rotate spaces"
+); # end: 71b541bb-819c-4dc6-a9c3-132ef9bb737b
+
+is( # begin: ef32601d-e9ef-4b29-b2b5-8971392282e6
+    caesar_cipher( "Testing 1 2 3 testing", 4 ),
+    "Xiwxmrk 1 2 3 xiwxmrk",
+    "rotate numbers"
+); # end: ef32601d-e9ef-4b29-b2b5-8971392282e6
+
+is( # begin: 32dd74f6-db2b-41a6-b02c-82eb4f93e549
+    caesar_cipher( "Let's eat, Grandma!", 21 ),
+    "Gzo'n zvo, Bmviyhv!",
+    "rotate punctuation"
+); # end: 32dd74f6-db2b-41a6-b02c-82eb4f93e549
+
+is( # begin: 9fb93fe6-42b0-46e6-9ec1-0bf0a062d8c9
+    caesar_cipher( "The quick brown fox jumps over the lazy dog.", 13 ),
+    "Gur dhvpx oebja sbk whzcf bire gur ynml qbt.",
+    "rotate all letters"
+); # end: 9fb93fe6-42b0-46e6-9ec1-0bf0a062d8c9
+
+done_testing;