!usrbinenv python3 The Bifid Cipher uses a Polybius Square to encipher a message in a way that makes it fairly difficult to decipher without knowing the secret. https:www.braingle.combrainteaserscodesbifid.php Return the pair of numbers that represents the given letter in the polybius square  np.arrayequalBifidCipher.lettertonumbers'a', 1,1 True  np.arrayequalBifidCipher.lettertonumbers'u', 4,5 True Return the letter corresponding to the position index1, index2 in the polybius square  BifidCipher.numberstoletter4, 5  u True  BifidCipher.numberstoletter1, 1  a True Return the encoded version of message according to the polybius cipher  BifidCipher.encode'testmessage'  'qtltbdxrxlk' True  BifidCipher.encode'Test Message'  'qtltbdxrxlk' True  BifidCipher.encode'test j'  BifidCipher.encode'test i' True Return the decoded version of message according to the polybius cipher  BifidCipher.decode'qtltbdxrxlk'  'testmessage' True
#!/usr/bin/env python3

"""
The Bifid Cipher uses a Polybius Square to encipher a message in a way that
makes it fairly difficult to decipher without knowing the secret.

https://www.braingle.com/brainteasers/codes/bifid.php
"""

import numpy as np

SQUARE = [
    ["a", "b", "c", "d", "e"],
    ["f", "g", "h", "i", "k"],
    ["l", "m", "n", "o", "p"],
    ["q", "r", "s", "t", "u"],
    ["v", "w", "x", "y", "z"],
]


class BifidCipher:
    def __init__(self) -> None:
        self.SQUARE = np.array(SQUARE)

    def letter_to_numbers(self, letter: str) -> np.ndarray:
        """
        Return the pair of numbers that represents the given letter in the
        polybius square

        >>> np.array_equal(BifidCipher().letter_to_numbers('a'), [1,1])
        True

        >>> np.array_equal(BifidCipher().letter_to_numbers('u'), [4,5])
        True
        """
        index1, index2 = np.where(letter == self.SQUARE)
        indexes = np.concatenate([index1 + 1, index2 + 1])
        return indexes

    def numbers_to_letter(self, index1: int, index2: int) -> str:
        """
        Return the letter corresponding to the position [index1, index2] in
        the polybius square

        >>> BifidCipher().numbers_to_letter(4, 5) == "u"
        True

        >>> BifidCipher().numbers_to_letter(1, 1) == "a"
        True
        """
        letter = self.SQUARE[index1 - 1, index2 - 1]
        return letter

    def encode(self, message: str) -> str:
        """
        Return the encoded version of message according to the polybius cipher

        >>> BifidCipher().encode('testmessage') == 'qtltbdxrxlk'
        True

        >>> BifidCipher().encode('Test Message') == 'qtltbdxrxlk'
        True

        >>> BifidCipher().encode('test j') == BifidCipher().encode('test i')
        True
        """
        message = message.lower()
        message = message.replace(" ", "")
        message = message.replace("j", "i")

        first_step = np.empty((2, len(message)))
        for letter_index in range(len(message)):
            numbers = self.letter_to_numbers(message[letter_index])

            first_step[0, letter_index] = numbers[0]
            first_step[1, letter_index] = numbers[1]

        second_step = first_step.reshape(2 * len(message))
        encoded_message = ""
        for numbers_index in range(len(message)):
            index1 = int(second_step[numbers_index * 2])
            index2 = int(second_step[(numbers_index * 2) + 1])
            letter = self.numbers_to_letter(index1, index2)
            encoded_message = encoded_message + letter

        return encoded_message

    def decode(self, message: str) -> str:
        """
        Return the decoded version of message according to the polybius cipher

        >>> BifidCipher().decode('qtltbdxrxlk') == 'testmessage'
        True
        """
        message = message.lower()
        message.replace(" ", "")
        first_step = np.empty(2 * len(message))
        for letter_index in range(len(message)):
            numbers = self.letter_to_numbers(message[letter_index])
            first_step[letter_index * 2] = numbers[0]
            first_step[letter_index * 2 + 1] = numbers[1]

        second_step = first_step.reshape((2, len(message)))
        decoded_message = ""
        for numbers_index in range(len(message)):
            index1 = int(second_step[0, numbers_index])
            index2 = int(second_step[1, numbers_index])
            letter = self.numbers_to_letter(index1, index2)
            decoded_message = decoded_message + letter

        return decoded_message
