Day 5: How About a Nice Game of Chess



In [1]:

    
with open("input/day5.txt", "r") as f:
    inputLines = [line for line in f]

doorId = bytes(inputLines[0].strip(), "utf-8")



In [2]:

    
import hashlib
import itertools

Implement a generator for 'interesting' hashes



In [3]:

    
def interestingHashes(prefix):
    for i in itertools.count():
        m = hashlib.md5()
        m.update(prefix + str(i).encode("utf-8"))
        h = m.hexdigest()
        if h.startswith("00000"):
            yield h

Part 1: Join the 5th character of each of the first 8 interesting hashes



In [4]:

    
def password1(prefix):
    return "".join(h[5] for h in itertools.islice(interestingHashes(prefix), 8))



In [5]:

    
password1(doorId)









    Out[5]:





'1a3099aa'

Part 2: More complex password algorithm

If the 5th character of an interesting hash is a digit between 0 and 7, it tells us a position in the password.
This position is assigned to the 6th character of the interesting hash.
An interesting hash is ignored if the position given by its 5th character has been seen already.



In [6]:

    
def password2(prefix):
    result = [None] * 8
    for h in interestingHashes(prefix):
        if h[5] in "01234567":
            pos = int(h[5])
            if result[pos] is None:
                result[pos] = h[6]
                if all(c is not None for c in result):
                    return "".join(result)



In [7]:

    
password2(doorId)









    Out[7]:





'694190cd'