feat: oct 2 level 4

python/oct2/level4/carrylessAdd.py

···
+from typing import List
+
+
+def carrylessAdd(x: int, y: int) -> int:
+    """Add two numbers without carrying."""
+    pos: List[int] = []
+    while x > 0 or y > 0:
+        sum = (x % 10 + y % 10) % 10
+        pos.append(sum)
+        x //= 10
+        y //= 10
+    num = 0
+    for idx, val in enumerate(pos):
+        num += val * 10**idx
+    return num
+
+
+print("Testing carrylessAdd()...", end="")
+assert carrylessAdd(8, 7) == 5
+assert carrylessAdd(785, 376) == 51
+assert carrylessAdd(0, 325) == 325
+assert carrylessAdd(30, 873) == 803
+assert carrylessAdd(873, 30) == 803
+assert carrylessAdd(100, 11) == 111
+print("Passed!")

python/oct2/level4/carrylessMultiply.py

···
+from typing import List
+
+
+def carrylessMultiply(x: int, y: int) -> int:
+    """Multiply 2 numbers without carrying"""
+    str_a = str(x)[::-1]
+    str_b = str(y)[::-1]
+
+    max_len = len(str_a) + len(str_b)
+    pos: List[int] = [0] * max_len
+    for i in range(len(str_a)):
+        for j in range(len(str_b)):
+            pnt = i + j
+            digit_a = int(str_a[i])
+            digit_b = int(str_b[j])
+            pos[pnt] += digit_a * digit_b
+            pos[pnt] %= 10
+    result_str = "".join(str(digit) for digit in pos[::-1]).lstrip("0") or "0"
+    return int(result_str)
+
+
+print("Testing carrylessMultiply()...", end="")
+assert carrylessMultiply(3, 3) == 9
+assert carrylessMultiply(4, 4) == 6
+assert carrylessMultiply(12345, 0) == 0
+assert carrylessMultiply(643, 59) == 417
+assert carrylessMultiply(6412, 387) == 807234
+print("Passed!")

python/oct2/level4/routeCipher.py

···
+def encodeRouteCipher(message: str, rows: int) -> str:
+    """Encode a message using the Route Cipher."""
+    cur_char = "z"
+    while len(message) % rows != 0:
+        message += cur_char
+        cur_char = chr(ord(cur_char) - 1)
+    str_cols = [message[i : i + rows] for i in range(0, len(message), rows)]
+    str_rows = ["".join(col) for col in zip(*str_cols)]
+    encoded_message = f"{rows}"
+    for idx, row in enumerate(str_rows):
+        if idx % 2 == 0:
+            encoded_message += row
+        else:
+            encoded_message += row[::-1]
+    return encoded_message
+
+
+def decodeRouteCipher(encodedMessage: str) -> str:
+    """Decode a message encoded using the Route Cipher."""
+    rows = int(encodedMessage[0])
+    rows_len = len(encodedMessage[1:]) // rows
+    encoded_message = encodedMessage[1:]
+    str_rows = [
+        encoded_message[i : i + rows_len]
+        for i in range(0, len(encoded_message), rows_len)
+    ]
+    str_rows = [row[::-1] if idx % 2 == 1 else row for idx, row in enumerate(str_rows)]
+    str_cols = ["".join(row) for row in zip(*str_rows)]
+    decoded_string = "".join(str_cols)
+    while decoded_string[-1].islower():
+        decoded_string = decoded_string[:-1]
+    return decoded_string
+
+
+print("Testing encodeRouteCipher()...", end="")
+assert encodeRouteCipher("ASECRETMESSAGE", 4) == "4AREGESESETSzyAMC"
+assert encodeRouteCipher("ASECRETMESSAGE", 3) == "3ACTSGESMRSEEEAz"
+assert encodeRouteCipher("ASECRETMESSAGE", 5) == "5AESATSEMGEECRSz"
+assert encodeRouteCipher("ANOTHERSECRET", 4) == "4AHETzCENORRyxEST"
+
+
+print("Testing decodeRouteCipher()...", end="")
+assert decodeRouteCipher("4AREGESESETSzyAMC") == "ASECRETMESSAGE"
+assert decodeRouteCipher("3ACTSGESMRSEEEAz") == "ASECRETMESSAGE"
+assert decodeRouteCipher("5AESATSEMGEECRSz") == "ASECRETMESSAGE"
+assert decodeRouteCipher("4AHETzCENORRyxEST") == "ANOTHERSECRET"
+message = "SECRETSTUFFGOESHERE"
+encodedMessage = encodeRouteCipher(message, 6)
+plaintext = decodeRouteCipher(encodedMessage)
+assert plaintext == message
+print("Passed!")