main.py

#

Part 1:

— Day 4: The Ideal Stocking Stuffer —

Santa needs help mining some AdventCoins (very similar to bitcoins) to use as gifts for all the economically forward-thinking little girls and boys.

To do this, he needs to find MD5 hashes which, in hexadecimal, start with at least five zeroes. The input to the MD5 hash is some secret key (your puzzle input, given below) followed by a number in decimal. To mine AdventCoins, you must find Santa the lowest positive number (no leading zeroes: 1, 2, 3, …) that produces such a hash.

import hashlib
import itertools
from typing import Callable, Iterable
#

For example:

def test_part1() -> None:
#

If your secret key is abcdef, the answer is 609043, because the MD5 hash of abcdef609043 starts with five zeroes (000001dbbfa...), and it is the lowest such number to do so.

    assert part1("abcdef") == 609043
#

If your secret key is pqrstuv, the lowest number it combines with to make an MD5 hash starting with five zeroes is 1048970; that is, the MD5 hash of pqrstuv1048970 looks like 000006136ef....

    assert part1("pqrstuv") == 1048970
#

Part 1 Solution: 


    

  

  

  

    

      

        #
      

      
    

    

      
def has_leading_zeros(zero_count: int, test_string: str) -> bool:
    return test_string.startswith("0" * zero_count)

    

  

  

  

    

      

        #
      

      
    

    

      
def modified_strings(input: str) -> Iterable[str]:
    for index in itertools.count():
        yield input + str(index)

    

  

  

  

    

      

        #
      

      
Append ever increasing integers to the input string until it MD5 hashes to a
value that satisfies the problem constraint.

    

    

      
def find_satisfactory_hash(
    input: str, constraint_function: Callable[[str], bool]
) -> int:

    

  

  

  

    

      

        #
      

      
    

    

      
    for index in itertools.count():
        test_string = input + str(index)
        hashed_string = hashlib.md5(test_string.encode()).hexdigest()
        if constraint_function(hashed_string):
            return index

    return -1

    

  

  

  

    

      

        #
      

      
Part 2:


Now find one that starts with six zeroes.

    

    

      
def part1(input: str) -> int:
    return find_satisfactory_hash(input, lambda s: has_leading_zeros(5, s))

    

  

  

  

    

      

        #
      

      
    

    

      

    

  

  

  

    

      

        #
      

      
 Part 2 Solution: 

    

    

      

    

  

  

  

    

      

        #
      

      
After completing part 1, I extracted the logic into a function that takes a
constraint function as an argument. This makes completing part 2 very
straightforward.

    

    

      

    

  

  

  

    

      

        #
      

      
    

    

      
def part2(input: str) -> int:
    return find_satisfactory_hash(input, lambda s: has_leading_zeros(6, s))


if __name__ == "__main__":
    puzzle_input = open("input.txt").read().rstrip()

    

  

  

  

    

      

        #
      

      
Print out part 1 solution

    

    

      
    print("Part 1:", part1(puzzle_input))

    

  

  

  

    

      

        #
      

      
Print out part 2 solution

    

    

      
    print("Part 2:", part2(puzzle_input))