Add medium exercises (#168)

Author: keiravillekode

config.json

@@ -299,10 +299,91 @@
         ],
         "difficulty": 4
       },
+      {
+        "slug": "luhn",
+        "name": "Luhn",
+        "uuid": "e83e333e-612a-4ec8-8d9f-da387327acdc",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 4
+      },
+      {
+        "slug": "robot-simulator",
+        "name": "Robot Simulator",
+        "uuid": "69868e6a-7e87-4cff-8f36-dd24c042e879",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 4
+      },
+      {
+        "slug": "sieve",
+        "name": "Sieve",
+        "uuid": "8b1fc515-71c2-436c-98dc-8789d25c7ddb",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 4
+      },
+      {
+        "slug": "space-age",
+        "name": "Space Age",
+        "uuid": "92fc6937-1b33-49f1-b66e-7ec7e3786906",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 4
+      },
+      {
+        "slug": "word-count",
+        "name": "Word Count",
+        "uuid": "f0a2b8f5-b244-4c35-86a7-9bf86843093c",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 4
+      },
       {
         "slug": "accumulate",
         "name": "Accumulate",
         "uuid": "8a373305-98c9-4b19-9011-085abe19cfed",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 5,
+        "status": "deprecated"
+      },
+      {
+        "slug": "affine-cipher",
+        "name": "Affine Cipher",
+        "uuid": "3e018380-7d24-403e-a951-b6f33ccc8afd",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 5
+      },
+      {
+        "slug": "anagram",
+        "name": "Anagram",
+        "uuid": "ec107dbf-5123-4405-934e-3e0846433fd0",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 5
+      },
+      {
+        "slug": "clock",
+        "name": "Clock",
+        "uuid": "2a606909-644b-4fd3-bd6c-bf0bb605a48d",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 5
+      },
+      {
+        "slug": "crypto-square",
+        "name": "Crypto Square",
+        "uuid": "c4b23be2-92e7-40ee-ad93-19f9f79eebc9",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 5
+      },
+      {
+        "slug": "list-ops",
+        "name": "List Ops",
+        "uuid": "9eb1ed19-7c5a-4c8f-98e3-7d99826deb18",
         "practices": [
           "quotations",
           "collections",
@@ -315,6 +396,38 @@
         ],
         "difficulty": 5
       },
+      {
+        "slug": "matching-brackets",
+        "name": "Matching Brackets",
+        "uuid": "afef364d-12dd-42fd-bbc8-f2c6228f0f53",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 5
+      },
+      {
+        "slug": "run-length-encoding",
+        "name": "Run-Length Encoding",
+        "uuid": "009090ef-d7fd-4ba5-9942-c6e686069e12",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 5
+      },
+      {
+        "slug": "square-root",
+        "name": "Square Root",
+        "uuid": "53cef38b-ad56-4462-bf37-48902fd3745c",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 5
+      },
+      {
+        "slug": "yacht",
+        "name": "Yacht",
+        "uuid": "c94bbdbb-cdfe-4b53-913c-fc7f705cc0d0",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 5
+      },
       {
         "slug": "all-your-base",
         "name": "All Your Base",
@@ -336,6 +449,62 @@
         "topics": [
           "math"
         ]
+      },
+      {
+        "slug": "game-of-life",
+        "name": "Conway's Game of Life",
+        "uuid": "36771f7d-aee3-44bd-a718-60efeaca3a8a",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 6
+      },
+      {
+        "slug": "ocr-numbers",
+        "name": "OCR Numbers",
+        "uuid": "725a35a9-b2ae-4c71-8dc9-a801a8699bd2",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 6
+      },
+      {
+        "slug": "rail-fence-cipher",
+        "name": "Rail Fence Cipher",
+        "uuid": "7f404c18-968e-41de-8067-7be5596a87ef",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 6
+      },
+      {
+        "slug": "say",
+        "name": "Say",
+        "uuid": "613a30e5-d545-40c7-b41e-f5ccb2c4ec88",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 6
+      },
+      {
+        "slug": "dominoes",
+        "name": "Dominoes",
+        "uuid": "cbbd1c5f-587b-4274-9889-1332d9446c63",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 7
+      },
+      {
+        "slug": "perfect-numbers",
+        "name": "Perfect Numbers",
+        "uuid": "0420eb1a-c607-4a65-8acb-aa3f60c01302",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 7
+      },
+      {
+        "slug": "rectangles",
+        "name": "Rectangles",
+        "uuid": "bfcd7856-38df-48e5-9bf1-438962ac44f8",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 7
       }
     ]
   },

exercises/practice/accumulate/accumulate/accumulate.factor

@@ -2,4 +2,4 @@ USING: kernel ;
 IN: accumulate
 
 :: accum ( seq quot: ( x -- y ) -- newseq )
-    "unimplemented" throw ;
+    "unimplemented" throw ; inline

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

@@ -0,0 +1,74 @@
+# Instructions
+
+Create an implementation of the affine cipher, an ancient encryption system created in the Middle East.
+
+The affine cipher is a type of monoalphabetic substitution cipher.
+Each character is mapped to its numeric equivalent, encrypted with a mathematical function and then converted to the letter relating to its new numeric value.
+Although all monoalphabetic ciphers are weak, the affine cipher is much stronger than the Atbash cipher, because it has many more keys.
+
+[//]: # " monoalphabetic as spelled by Merriam-Webster, compare to polyalphabetic "
+
+## Encryption
+
+The encryption function is:
+
+```text
+E(x) = (ai + b) mod m
+```
+
+Where:
+
+- `i` is the letter's index from `0` to the length of the alphabet - 1.
+- `m` is the length of the alphabet.
+  For the Latin alphabet `m` is `26`.
+- `a` and `b` are integers which make up the encryption key.
+
+Values `a` and `m` must be _coprime_ (or, _relatively prime_) for automatic decryption to succeed, i.e., they have number `1` as their only common factor (more information can be found in the [Wikipedia article about coprime integers][coprime-integers]).
+In case `a` is not coprime to `m`, your program should indicate that this is an error.
+Otherwise it should encrypt or decrypt with the provided key.
+
+For the purpose of this exercise, digits are valid input but they are not encrypted.
+Spaces and punctuation characters are excluded.
+Ciphertext is written out in groups of fixed length separated by space, the traditional group size being `5` letters.
+This is to make it harder to guess encrypted text based on word boundaries.
+
+## Decryption
+
+The decryption function is:
+
+```text
+D(y) = (a^-1)(y - b) mod m
+```
+
+Where:
+
+- `y` is the numeric value of an encrypted letter, i.e., `y = E(x)`
+- it is important to note that `a^-1` is the modular multiplicative inverse (MMI) of `a mod m`
+- the modular multiplicative inverse only exists if `a` and `m` are coprime.
+
+The MMI of `a` is `x` such that the remainder after dividing `ax` by `m` is `1`:
+
+```text
+ax mod m = 1
+```
+
+More information regarding how to find a Modular Multiplicative Inverse and what it means can be found in the [related Wikipedia article][mmi].
+
+## General Examples
+
+- Encrypting `"test"` gives `"ybty"` with the key `a = 5`, `b = 7`
+- Decrypting `"ybty"` gives `"test"` with the key `a = 5`, `b = 7`
+- Decrypting `"ybty"` gives `"lqul"` with the wrong key `a = 11`, `b = 7`
+- Decrypting `"kqlfd jzvgy tpaet icdhm rtwly kqlon ubstx"` gives `"thequickbrownfoxjumpsoverthelazydog"` with the key `a = 19`, `b = 13`
+- Encrypting `"test"` with the key `a = 18`, `b = 13` is an error because `18` and `26` are not coprime
+
+## Example of finding a Modular Multiplicative Inverse (MMI)
+
+Finding MMI for `a = 15`:
+
+- `(15 * x) mod 26 = 1`
+- `(15 * 7) mod 26 = 1`, ie. `105 mod 26 = 1`
+- `7` is the MMI of `15 mod 26`
+
+[mmi]: https://en.wikipedia.org/wiki/Modular_multiplicative_inverse
+[coprime-integers]: https://en.wikipedia.org/wiki/Coprime_integers

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

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "keiravillekode"
+  ],
+  "files": {
+    "solution": [
+      "affine-cipher/affine-cipher.factor"
+    ],
+    "test": [
+      "affine-cipher/affine-cipher-tests.factor"
+    ],
+    "example": [
+      ".meta/example.factor"
+    ]
+  },
+  "blurb": "Create an implementation of the Affine cipher, an ancient encryption algorithm from the Middle East.",
+  "source": "Wikipedia",
+  "source_url": "https://en.wikipedia.org/wiki/Affine_cipher"
+}

exercises/practice/affine-cipher/.meta/example.factor

@@ -0,0 +1,30 @@
+USING: combinators grouping kernel locals math math.functions
+ranges sequences sets strings unicode ;
+IN: affine-cipher
+
+: check-coprime ( a -- a )
+    dup 26 gcd nip 1 = [ "a and m must be coprime." throw ] unless ;
+
+: mmi ( a -- a^-1 )
+    26 [1..b] [ over * 26 mod 1 = ] find nip nip ;
+
+: group5 ( str -- str ) 5 group " " join ;
+
+:: encode ( phrase a b -- cipher )
+    a check-coprime drop
+    phrase >lower
+    [ [ Letter? ] [ digit? ] bi or ] filter
+    [| ch |
+        ch digit?
+        [ ch ]
+        [ ch CHAR: a - a * b + 26 mod CHAR: a + ] if
+    ] map group5 ;
+
+:: decode ( phrase a b -- plain )
+    a check-coprime mmi :> a-inv
+    phrase " " without
+    [| ch |
+        ch digit?
+        [ ch ]
+        [ ch CHAR: a - b - a-inv * 26 mod dup 0 < [ 26 + ] when CHAR: a + ] if
+    ] map ;

exercises/practice/affine-cipher/.meta/generator.jl

@@ -0,0 +1,17 @@
+module AffineCipher
+
+function gen_test_case(case)
+    phrase = escape_factor(case["input"]["phrase"])
+    a = Int(case["input"]["key"]["a"])
+    b = Int(case["input"]["key"]["b"])
+    prop = case["property"]
+    expected = case["expected"]
+    if expected isa Dict
+        msg = expected["error"]
+        return """[ "$(phrase)" $(a) $(b) $(prop) ]\n[ "$(msg)" = ] must-fail-with"""
+    else
+        return """{ "$(expected)" }\n[ "$(phrase)" $(a) $(b) $(prop) ] unit-test"""
+    end
+end
+
+end

exercises/practice/affine-cipher/.meta/supplements.json

@@ -0,0 +1,8 @@
+[
+  {
+    "description": "encode boundary characters",
+    "property": "encode",
+    "input": {"phrase": "/09:@AMNZ[`amnz{", "key": {"a": 25, "b": 12}},
+    "expected": "09maz nmazn"
+  }
+]