Added rail fence cipher (TheAlgorithms#3188)

* Added rail fence cipher

* Update rail_fence_cipher.py

* Update rail_fence_cipher.py

Author: PTK12

Diff for: ciphers/rail_fence_cipher.py

@@ -0,0 +1,102 @@
+""" https://en.wikipedia.org/wiki/Rail_fence_cipher """
+
+
+def encrypt(input_string: str, key: int) -> str:
+    """
+    Shuffles the character of a string by placing each of them
+    in a grid (the height is dependent on the key) in a zigzag
+    formation and reading it left to right.
+
+    >>> encrypt("Hello World", 4)
+    'HWe olordll'
+
+    >>> encrypt("This is a message", 0)
+    Traceback (most recent call last):
+        ...
+    ValueError: Height of grid can't be 0 or negative
+
+    >>> encrypt(b"This is a byte string", 5)
+    Traceback (most recent call last):
+        ...
+    TypeError: sequence item 0: expected str instance, int found
+    """
+    grid = [[] for _ in range(key)]
+    lowest = key - 1
+
+    if key <= 0:
+        raise ValueError("Height of grid can't be 0 or negative")
+    if key == 1 or len(input_string) <= key:
+        return input_string
+
+    for position, character in enumerate(input_string):
+        num = position % (lowest * 2)  # puts it in bounds
+        num = min(num, lowest * 2 - num)  # creates zigzag pattern
+        grid[num].append(character)
+    grid = ["".join(row) for row in grid]
+    output_string = "".join(grid)
+
+    return output_string
+
+
+def decrypt(input_string: str, key: int) -> str:
+    """
+    Generates a template based on the key and fills it in with
+    the characters of the input string and then reading it in
+    a zigzag formation.
+
+    >>> decrypt("HWe olordll", 4)
+    'Hello World'
+
+    >>> decrypt("This is a message", -10)
+    Traceback (most recent call last):
+        ...
+    ValueError: Height of grid can't be 0 or negative
+
+    >>> decrypt("My key is very big", 100)
+    'My key is very big'
+    """
+    grid = []
+    lowest = key - 1
+
+    if key <= 0:
+        raise ValueError("Height of grid can't be 0 or negative")
+    if key == 1:
+        return input_string
+
+    temp_grid = [[] for _ in range(key)]  # generates template
+    for position in range(len(input_string)):
+        num = position % (lowest * 2)  # puts it in bounds
+        num = min(num, lowest * 2 - num)  # creates zigzag pattern
+        temp_grid[num].append("*")
+
+    counter = 0
+    for row in temp_grid:  # fills in the characters
+        splice = input_string[counter : counter + len(row)]
+        grid.append([character for character in splice])
+        counter += len(row)
+
+    output_string = ""  # reads as zigzag
+    for position in range(len(input_string)):
+        num = position % (lowest * 2)  # puts it in bounds
+        num = min(num, lowest * 2 - num)  # creates zigzag pattern
+        output_string += grid[num][0]
+        grid[num].pop(0)
+    return output_string
+
+
+def bruteforce(input_string: str) -> dict:
+    """Uses decrypt function by guessing every key
+
+    >>> bruteforce("HWe olordll")[4]
+    'Hello World'
+    """
+    results = {}
+    for key_guess in range(1, len(input_string)):  # tries every key
+        results[key_guess] = decrypt(input_string, key_guess)
+    return results
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()