def encodeSimpleCipher(s: str) -> str:
    """
    Encode a string using this formula.
        - s[i] = 2*i
        - if 2*i > len(s), s[i] = (2*i) % len(s)
    """
    encoded = list(s)
    for i in range(len(s)):
        j = (2 * i) % len(s)
        cj = encoded[j]
        encoded[j] = encoded[i]
        encoded[i] = cj
    return "".join(encoded)


def decodeSimpleCipher(s: str) -> str:
    """Decode a string encoded from encodeSimpleCipher"""
    decoded = list(s)
    for i in range(len(s) - 1, -1, -1):
        j = (2 * i) % len(s)
        cj = decoded[j]
        decoded[j] = decoded[i]
        decoded[i] = cj
    return "".join(decoded)


print("Testing encodeSimpleCipher()...", end="")
assert encodeSimpleCipher("AB") == "BA"
assert encodeSimpleCipher("ABC") == "ABC"
assert encodeSimpleCipher("ABCD") == "BCDA"
assert encodeSimpleCipher("ABCDEFGH") == "BCFGDEHA"
assert encodeSimpleCipher("SECRET MESSAGE") == "MCE SSTSAEREEG"
assert (
    encodeSimpleCipher("THIS IS A LONGER SECRET MESSAGE JUST FOR YOU!")
    == "T  SAENG SR MGARJ  H U!SSTE TFECORIIEYSELUOOS"
)
print("Passed!")


print("Testing decodeSimpleCipher()...", end="")
assert decodeSimpleCipher("BA") == "AB"
assert decodeSimpleCipher("ABC") == "ABC"
assert decodeSimpleCipher("BCDA") == "ABCD"
assert decodeSimpleCipher("BCFGDEHA") == "ABCDEFGH"
assert decodeSimpleCipher("MCE SSTSAEREEG") == "SECRET MESSAGE"
assert (
    decodeSimpleCipher("T  SAENG SR MGARJ  H U!SSTE TFECORIIEYSELUOOS")
    == "THIS IS A LONGER SECRET MESSAGE JUST FOR YOU!"
)
print("Passed!")