adventofcode/2016/day05/problem

Advent of Code

--- Day 5: How About a Nice Game of Chess? ---

   You are faced with a security door designed by Easter Bunny engineers that
   seem to have acquired most of their security knowledge by watching hacking
   movies.

   The eight-character password for the door is generated one character at a
   time by finding the MD5 hash of some Door ID (your puzzle input) and an
   increasing integer index (starting with 0).

   A hash indicates the next character in the password if its hexadecimal
   representation starts with five zeroes. If it does, the sixth character in
   the hash is the next character of the password.

   For example, if the Door ID is abc:

     • The first index which produces a hash that starts with five zeroes is
       3231929, which we find by hashing abc3231929; the sixth character of the
       hash, and thus the first character of the password, is 1.

     • 5017308 produces the next interesting hash, which starts with
       000008f82..., so the second character of the password is 8.

     • The third time a hash starts with five zeroes is for abc5278568,
       discovering the character f.

   In this example, after continuing this search a total of eight times, the
   password is 18f47a30.

   Given the actual Door ID, what is the password?

   Your puzzle answer was 4543c154.

--- Part Two ---

   As the door slides open, you are presented with a second door that uses a
   slightly more inspired security mechanism. Clearly unimpressed by the last
   version (in what movie is the password decrypted in order?!), the Easter
   Bunny engineers have worked out a better solution.

   Instead of simply filling in the password from left to right, the hash now
   also indicates the position within the password to fill. You still look for
   hashes that begin with five zeroes; however, now, the sixth character
   represents the position (0-7), and the seventh character is the character to
   put in that position.

   A hash result of 000001f means that f is the second character in the
   password. Use only the first result for each position, and ignore invalid
   positions.

   For example, if the Door ID is abc:

     • The first interesting hash is from abc3231929, which produces
     0000015...; so, 5 goes in position 1: _5______.

     • In the previous method, 5017308 produced an interesting hash; however,
     it is ignored, because it specifies an invalid position (8).

     • The second interesting hash is at index 5357525, which produces
     000004e...; so, e goes in position 4: _5__e___.

   You almost choke on your popcorn as the final character falls into place,
   producing the password 05ace8e3.

   Given the actual Door ID and this new method, what is the password? Be extra
   proud of your solution if it uses a cinematic "decrypting" animation.

   Your puzzle answer was 1050cbbd.

   Your puzzle input was ojvtpuvg.

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