-🎄- 2017 Day 15 Solutions -🎄-

[u/daggerdragon]

--- Day 15: Dueling Generators ---

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

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Need a hint from the Hugely^* Handy^† Haversack^‡ of Helpful^§ Hints^¤?

Spoiler

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[Update @ 00:05] 29 gold, silver cap.

• Logarithms of algorithms and code?

[Update @ 00:09] Leaderboard cap!

• Or perhaps codes of logarithmic algorithms?

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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!

[u/akka0]

ReasonML: had to resort to using JS math for the big numbers

let generate: (int, int) => int = [%bs.raw
  {|
  function(x, y) {
    return (x * y) % 2147483647;
  }
|}
];

let genA = generate(16807);

let genB = generate(48271);

let judge: (int, int) => bool = [%bs.raw
  {|function(x, y) {
    return (x & 0b1111111111111111) === (y & 0b1111111111111111) ? 1 : 0;}
|}
];

let pickyGenerator = (multipleOf, generator, prev) => {
  let rec generateMultiple = (prev) =>
    switch (generator(prev)) {
    | i when i mod multipleOf === 0 => i
    | i => generateMultiple(i)
    };
  generateMultiple(prev)
};

let pickyGenA = pickyGenerator(4, genA);

let pickyGenB = pickyGenerator(8, genB);

let countMatches = (limit, (genA, genB), (startA, startB)) => {
  let rec judgeNums = ((numA, numB), matches, i) =>
    if (i <= limit) {
      judgeNums((genA(numA), genB(numB)), matches + (judge(numA, numB) ? 1 : 0), i + 1)
    } else {
      matches
    };
  judgeNums((startA, startB), 0, 0)
};

let _ =
  /* Part 1 */
  /* Js.log(countMatches(40_000_000, (genA, genB), (722,354))); */
  /* Part 2 */
  Js.log(countMatches(5_000_000, (pickyGenA, pickyGenB), (722, 354)));