the ideal stocking stuffer

approach

the secret key is read from stdin and nonces are tried in order, hashing key + nonce with md5 until the digest starts with enough zeros.

the check works on the raw digest bytes instead of the hex string: every two hex zeros are one zero byte, and an odd leftover zero means the next byte is below 0x10. part 1 asks for 5 zeros and part 2 for 6, with the same function.

the trick

count leading hex zeros on the raw bytes: whole zero bytes first, then a half byte.

def k_prefix_zeros(digest, k):
    i = 0
    while k >= 2:
        if digest[i] != 0:
            return False
        k -= 2
        i += 1
    if k > 0:
        return digest[i] < 0x10
    return True