| 1 | 1 | def encode(plain_text: str, a: int, b: int) -> str: |
| 2 | pass | |
| 2 | m = 26 # Size of the alphabet | |
| 3 | ||
| 4 | # Edge Case: Check if a and m are coprime | |
| 5 | if gcd(a, m) != 1: | |
| 6 | raise ValueError("a and m must be coprime.") | |
| 7 | ||
| 8 | result = [] | |
| 9 | plain_text = plain_text.lower() | |
| 10 | ||
| 11 | for char in plain_text: | |
| 12 | # Edge Case: Skip non-alphanumeric characters | |
| 13 | if not char.isalnum(): | |
| 14 | continue | |
| 15 | ||
| 16 | if char.isalpha(): | |
| 17 | # Edge Case: Encrypt alphabetic characters | |
| 18 | i = ord(char) - ord('a') | |
| 19 | encrypted_index = (a * i + b) % m | |
| 20 | result.append(chr(encrypted_index + ord('a'))) | |
| 21 | else: | |
| 22 | # Edge Case: Keep digits as they are | |
| 23 | result.append(char) | |
| 24 | ||
| 25 | # Edge Case: Group result into chunks of 5 characters | |
| 26 | grouped_result = [] | |
| 27 | for i in range(0, len(result), 5): | |
| 28 | grouped_result.append(''.join(result[i:i+5])) | |
| 29 | ||
| 30 | return ' '.join(grouped_result) | |
| 3 | 31 | |
| 4 | 32 | |
| 5 | 33 | def decode(ciphered_text: str, a: int, b: int) -> str: |
| 6 | pass | |
| 34 | m = 26 # Size of the alphabet | |
| 35 | ||
| 36 | # Edge Case: Check if a and m are coprime | |
| 37 | if gcd(a, m) != 1: | |
| 38 | raise ValueError("a and m must be coprime.") | |
| 39 | ||
| 40 | # Edge Case: Calculate modular multiplicative inverse of a | |
| 41 | a_inv = mod_inverse(a, m) | |
| 42 | ||
| 43 | result = [] | |
| 44 | ciphered_text = ciphered_text.replace(' ', '').lower() | |
| 45 | ||
| 46 | for char in ciphered_text: | |
| 47 | if char.isalpha(): | |
| 48 | # Edge Case: Decrypt alphabetic characters | |
| 49 | y = ord(char) - ord('a') | |
| 50 | decrypted_index = (a_inv * (y - b)) % m | |
| 51 | result.append(chr(decrypted_index + ord('a'))) | |
| 52 | else: | |
| 53 | # Edge Case: Keep digits as they are | |
| 54 | result.append(char) | |
| 55 | ||
| 56 | return ''.join(result) | |
| 57 | ||
| 58 | ||
| 59 | def gcd(a: int, b: int) -> int: | |
| 60 | # Edge Case: Calculate greatest common divisor | |
| 61 | while b: | |
| 62 | a, b = b, a % b | |
| 63 | return a | |
| 64 | ||
| 65 | ||
| 66 | def mod_inverse(a: int, m: int) -> int: | |
| 67 | # Edge Case: Calculate modular multiplicative inverse | |
| 68 | # Add iteration limit to prevent potential infinite loop | |
| 69 | for x in range(1, m + 1): | |
| 70 | if (a * x) % m == 1: | |
| 71 | return x | |
| 72 | # This should never happen if gcd(a, m) == 1 | |
| 73 | raise ValueError("Modular inverse does not exist") | |
| 74 | # Handled Edge Cases: a and m not coprime, non-alphanumeric characters, alphabetic encryption, digit handling, grouping into chunks, modular multiplicative inverse calculation, alphabetic decryption |
| Test Name | Status |
|---|---|
test_decode_a_sentence | Pass |
test_decode_all_the_letters | Pass |
test_decode_exercism | Pass |
test_decode_numbers | Pass |
test_decode_with_a_not_coprime_to_m | Pass |
test_decode_with_no_spaces_in_input | Pass |
test_decode_with_too_many_spaces | Pass |
test_encode_all_the_letters | Pass |
test_encode_deep_thought | Pass |
test_encode_mindblowingly | Pass |
test_encode_no | Pass |
test_encode_numbers | Pass |
test_encode_o_m_g | Pass |
test_encode_omg | Pass |
test_encode_with_a_not_coprime_to_m | Pass |
test_encode_yes | Pass |
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