hill_cipher.py: gcd() -> greatest_common_divisor() (#1997)

* hill_cipher.py: gcd() -> greatest_common_divisor()

* fixup! Format Python code with psf/black push

* import string

* updating DIRECTORY.md

* Change matrix to array

Add more tests

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
Co-authored-by: John Law <johnlaw.po@gmail.com>

DIRECTORY.md

@@ -603,6 +603,7 @@
   * [Shell Sort](https://github.com/TheAlgorithms/Python/blob/master/sorts/shell_sort.py)
   * [Sleep Sort](https://github.com/TheAlgorithms/Python/blob/master/sorts/sleep_sort.py)
   * [Stooge Sort](https://github.com/TheAlgorithms/Python/blob/master/sorts/stooge_sort.py)
+  * [Strand Sort](https://github.com/TheAlgorithms/Python/blob/master/sorts/strand_sort.py)
   * [Tim Sort](https://github.com/TheAlgorithms/Python/blob/master/sorts/tim_sort.py)
   * [Topological Sort](https://github.com/TheAlgorithms/Python/blob/master/sorts/topological_sort.py)
   * [Tree Sort](https://github.com/TheAlgorithms/Python/blob/master/sorts/tree_sort.py)

ciphers/hill_cipher.py

@@ -1,10 +1,9 @@
 """
 
 Hill Cipher:
-The below defined class 'HillCipher' implements the Hill Cipher algorithm.
+The 'HillCipher' class below implements the Hill Cipher algorithm which uses
-The Hill Cipher is an algorithm that implements modern linear algebra techniques
+modern linear algebra techniques to encode and decode text using an encryption
-In this algorithm, you have an encryption key matrix. This is what will be used
+key matrix.
-in encoding and decoding your text.
 
 Algorithm:
 Let the order of the encryption key be N (as it is a square matrix).
@@ -24,12 +23,11 @@ Constraints:
 The determinant of the encryption key matrix must be relatively prime w.r.t 36.
 
 Note:
-The algorithm implemented in this code considers only alphanumerics in the text.
+This implementation only considers alphanumerics in the text.  If the length of
-If the length of the text to be encrypted is not a multiple of the
+the text to be encrypted is not a multiple of the break key(the length of one
-break key(the length of one batch of letters),the last character of the text
+batch of letters), the last character of the text is added to the text until the
-is added to the text until the length of the text reaches a multiple of
+length of the text reaches a multiple of the break_key. So the text after
-the break_key. So the text after decrypting might be a little different than
+decrypting might be a little different than the original text.
-the original text.
 
 References:
 https://apprendre-en-ligne.net/crypto/hill/Hillciph.pdf
@@ -38,67 +36,66 @@ https://www.youtube.com/watch?v=4RhLNDqcjpA
 
 """
 
+import string
 import numpy
 
 
-def gcd(a: int, b: int) -> int:
+def greatest_common_divisor(a: int, b: int) -> int:
     """
-    >>> gcd(4, 8)
+    >>> greatest_common_divisor(4, 8)
     4
-    >>> gcd(8, 4)
+    >>> greatest_common_divisor(8, 4)
     4
-    >>> gcd(4, 7)
+    >>> greatest_common_divisor(4, 7)
     1
-    >>> gcd(0, 10)
+    >>> greatest_common_divisor(0, 10)
     10
     """
-    if a == 0:
+    return b if a == 0 else greatest_common_divisor(b % a, a)
-        return b
-    return gcd(b % a, a)
 
 
 class HillCipher:
-    key_string = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
+    key_string = string.ascii_uppercase + string.digits
     # This cipher takes alphanumerics into account
     # i.e. a total of 36 characters
 
     # take x and return x % len(key_string)
     modulus = numpy.vectorize(lambda x: x % 36)
 
-    toInt = numpy.vectorize(lambda x: round(x))
+    to_int = numpy.vectorize(lambda x: round(x))
 
     def __init__(self, encrypt_key):
         """
-        encrypt_key is an NxN numpy matrix
+        encrypt_key is an NxN numpy array
         """
         self.encrypt_key = self.modulus(encrypt_key)  # mod36 calc's on the encrypt key
         self.check_determinant()  # validate the determinant of the encryption key
         self.decrypt_key = None
         self.break_key = encrypt_key.shape[0]
 
-    def replaceLetters(self, letter: str) -> int:
+    def replace_letters(self, letter: str) -> int:
         """
-        >>> hill_cipher = HillCipher(numpy.matrix([[2, 5], [1, 6]]))
+        >>> hill_cipher = HillCipher(numpy.array([[2, 5], [1, 6]]))
-        >>> hill_cipher.replaceLetters('T')
+        >>> hill_cipher.replace_letters('T')
         19
-        >>> hill_cipher.replaceLetters('0')
+        >>> hill_cipher.replace_letters('0')
         26
         """
         return self.key_string.index(letter)
 
-    def replaceNumbers(self, num: int) -> str:
+    def replace_digits(self, num: int) -> str:
         """
-        >>> hill_cipher = HillCipher(numpy.matrix([[2, 5], [1, 6]]))
+        >>> hill_cipher = HillCipher(numpy.array([[2, 5], [1, 6]]))
-        >>> hill_cipher.replaceNumbers(19)
+        >>> hill_cipher.replace_digits(19)
         'T'
-        >>> hill_cipher.replaceNumbers(26)
+        >>> hill_cipher.replace_digits(26)
         '0'
         """
         return self.key_string[round(num)]
 
     def check_determinant(self) -> None:
         """
-        >>> hill_cipher = HillCipher(numpy.matrix([[2, 5], [1, 6]]))
+        >>> hill_cipher = HillCipher(numpy.array([[2, 5], [1, 6]]))
         >>> hill_cipher.check_determinant()
         """
         det = round(numpy.linalg.det(self.encrypt_key))
@@ -107,19 +104,20 @@ class HillCipher:
             det = det % len(self.key_string)
 
         req_l = len(self.key_string)
-        if gcd(det, len(self.key_string)) != 1:
+        if greatest_common_divisor(det, len(self.key_string)) != 1:
             raise ValueError(
                 f"determinant modular {req_l} of encryption key({det}) is not co prime w.r.t {req_l}.\nTry another key."
             )
 
     def process_text(self, text: str) -> str:
         """
-        >>> hill_cipher = HillCipher(numpy.matrix([[2, 5], [1, 6]]))
+        >>> hill_cipher = HillCipher(numpy.array([[2, 5], [1, 6]]))
         >>> hill_cipher.process_text('Testing Hill Cipher')
         'TESTINGHILLCIPHERR'
+        >>> hill_cipher.process_text('hello')
+        'HELLOO'
         """
-        text = list(text.upper())
+        chars = [char for char in text.upper() if char in self.key_string]
-        chars = [char for char in text if char in self.key_string]
 
         last = chars[-1]
         while len(chars) % self.break_key != 0:
@@ -129,22 +127,24 @@ class HillCipher:
 
     def encrypt(self, text: str) -> str:
         """
-        >>> hill_cipher = HillCipher(numpy.matrix([[2, 5], [1, 6]]))
+        >>> hill_cipher = HillCipher(numpy.array([[2, 5], [1, 6]]))
         >>> hill_cipher.encrypt('testing hill cipher')
         'WHXYJOLM9C6XT085LL'
+        >>> hill_cipher.encrypt('hello')
+        '85FF00'
         """
         text = self.process_text(text.upper())
         encrypted = ""
 
         for i in range(0, len(text) - self.break_key + 1, self.break_key):
             batch = text[i : i + self.break_key]
-            batch_vec = [self.replaceLetters(char) for char in batch]
+            batch_vec = [self.replace_letters(char) for char in batch]
-            batch_vec = numpy.matrix([batch_vec]).T
+            batch_vec = numpy.array([batch_vec]).T
             batch_encrypted = self.modulus(self.encrypt_key.dot(batch_vec)).T.tolist()[
                 0
             ]
             encrypted_batch = "".join(
-                self.replaceNumbers(num) for num in batch_encrypted
+                self.replace_digits(num) for num in batch_encrypted
             )
             encrypted += encrypted_batch
 
@@ -152,10 +152,10 @@ class HillCipher:
 
     def make_decrypt_key(self):
         """
-        >>> hill_cipher = HillCipher(numpy.matrix([[2, 5], [1, 6]]))
+        >>> hill_cipher = HillCipher(numpy.array([[2, 5], [1, 6]]))
         >>> hill_cipher.make_decrypt_key()
-        matrix([[ 6., 25.],
+        array([[ 6., 25.],
-                [ 5., 26.]])
+               [ 5., 26.]])
         """
         det = round(numpy.linalg.det(self.encrypt_key))
 
@@ -173,13 +173,15 @@ class HillCipher:
             * numpy.linalg.inv(self.encrypt_key)
         )
 
-        return self.toInt(self.modulus(inv_key))
+        return self.to_int(self.modulus(inv_key))
 
     def decrypt(self, text: str) -> str:
         """
-        >>> hill_cipher = HillCipher(numpy.matrix([[2, 5], [1, 6]]))
+        >>> hill_cipher = HillCipher(numpy.array([[2, 5], [1, 6]]))
         >>> hill_cipher.decrypt('WHXYJOLM9C6XT085LL')
         'TESTINGHILLCIPHERR'
+        >>> hill_cipher.decrypt('85FF00')
+        'HELLOO'
         """
         self.decrypt_key = self.make_decrypt_key()
         text = self.process_text(text.upper())
@@ -187,13 +189,13 @@ class HillCipher:
 
         for i in range(0, len(text) - self.break_key + 1, self.break_key):
             batch = text[i : i + self.break_key]
-            batch_vec = [self.replaceLetters(char) for char in batch]
+            batch_vec = [self.replace_letters(char) for char in batch]
-            batch_vec = numpy.matrix([batch_vec]).T
+            batch_vec = numpy.array([batch_vec]).T
             batch_decrypted = self.modulus(self.decrypt_key.dot(batch_vec)).T.tolist()[
                 0
             ]
             decrypted_batch = "".join(
-                self.replaceNumbers(num) for num in batch_decrypted
+                self.replace_digits(num) for num in batch_decrypted
             )
             decrypted += decrypted_batch
 
@@ -206,19 +208,13 @@ def main():
 
     print("Enter each row of the encryption key with space separated integers")
     for i in range(N):
-        row = list(map(int, input().split()))
+        row = [int(x) for x in input().split()]
         hill_matrix.append(row)
 
-    hc = HillCipher(numpy.matrix(hill_matrix))
+    hc = HillCipher(numpy.array(hill_matrix))
 
     print("Would you like to encrypt or decrypt some text? (1 or 2)")
-    option = input(
+    option = input("\n1. Encrypt\n2. Decrypt\n")
-        """
-1. Encrypt
-2. Decrypt
-"""
-    )
-
     if option == "1":
         text_e = input("What text would you like to encrypt?: ")
         print("Your encrypted text is:")
@@ -231,6 +227,7 @@ def main():
 
 if __name__ == "__main__":
     import doctest
+
     doctest.testmod()
 
     main()