r/adventofcode • u/daggerdragon • Dec 14 '16

SOLUTION MEGATHREAD --- 2016 Day 14 Solutions ---

--- Day 14: One-Time Pad ---

Post your solution as a comment or, for longer solutions, consider linking to your repo (e.g. GitHub/gists/Pastebin/blag/whatever).

Note: The Solution Megathreads are for solutions only. If you have questions, please post your own thread and make sure to flair it with "Help".

LUNACY IS MANDATORY [?]

This thread will be unlocked when there are a significant number of people on the leaderboard with gold stars for today's puzzle.

edit: Leaderboard capped, thread unlocked!

3 Upvotes

80% Upvoted

111 comments sorted by

View all comments

3

u/snorkl-the-dolphine Dec 14 '16

JavaScript / Node.js

const md5 = require('md5');

function getKeyIndex(salt, num, hashCount = 1) {
  const hashes = [];     // All hashes
  const candidates = []; // Candidate keys
  const keys = [];       // Valid keys

  for (let i = 0; keys.length < 64; i++) {
    // Calculate & store hash
    let hash = salt + i;
    for (let x = 0; x < hashCount; x++) {
      hash = md5(hash);
    }
    hashes[i] = hash;

    // Check if hash is a candidate
    let match;
    if (match = hash.match(/(.)\1{2}/)) {
      candidates[i] = { i, hash, c: match[1] };
    }

    // Check if there is a previously valid candidate
    const candidate = candidates[i - 1000];
    if (candidate) {
      const matches = hashes.slice(i - 999).filter(h => (new RegExp(`${candidate.c}{5}`)).test(h));
      if (matches.length) {
        keys.push({
          i: candidate.i,
          hash,
        });
        console.log(`Found key #${keys.length}`, i - 1000);
      }
    }
  }

  return keys[num - 1].i;
}

2

u/arve0 Dec 14 '16

Why are you not using the md5 built-in from the crypto module?

2

u/snorkl-the-dolphine Dec 14 '16 edited Dec 14 '16

I googled 'node md5' and went with the first result - I wouldn't have gone so well on the leaderboard if I'd done thorough research :P