Day 9: Mirage Maintenance

Megathread guidelines

  • Keep top level comments as only solutions, if you want to say something other than a solution put it in a new post. (replies to comments can be whatever)
  • Code block support is not fully rolled out yet but likely will be in the middle of the event. Try to share solutions as both code blocks and using something such as https://topaz.github.io/paste/ , pastebin, or github (code blocks to future proof it for when 0.19 comes out and since code blocks currently function in some apps and some instances as well if they are running a 0.19 beta)

FAQ

🔒 Thread is locked until there’s at least 100 2 star entries on the global leaderboard

🔓 Unlocked after 5 mins

  • SteveDinn
    2·
    11 months ago

    C#

    Used recursion to determine the differences for part 1 and then extracted the variations in processing from predicting the end vs. the beginning of the history and passed them in as Func variables to the recursive method.

    Day 9

    • SteveDinn
      2·
      11 months ago

      Snippet:

              static void Part1(string data)
        {
            var result = ParseInput(data)
                .Select(history => ProcessHistory(history, g => g.Length - 1, (a, b) => a + b))
                .Sum();

            Console.WriteLine(result);
        }

        static void Part2(string data)
        {
            var result = ParseInput(data)
                .Select(history => ProcessHistory(history, g => 0, (a, b) => a - b))
                .Sum();

            Console.WriteLine(result);
        }

        static int ProcessHistory(
            int[] history,
            Func guessIndex,
            Func collateGuess)
        {
            bool allZeros = true;

            var diffs = new int[history.Length - 1];
            for (int i = 0; i < diffs.Length; i++)
            {
                var diff = history[i + 1] - history[i];
                diffs[i] = diff;
                allZeros = allZeros && (diff == 0);
            }

            var guess = history[guessIndex(history)];

            if (!allZeros)
            {
                guess = collateGuess(
                    guess,
                    ProcessHistory(diffs, guessIndex, collateGuess));
            }

            return guess;
        }