Advent of Code - 2024 - Day 11

var timer = System.Diagnostics.Stopwatch.StartNew();
var stones = (await File.ReadAllTextAsync("input.txt")).Split(' ').ToDictionary(long.Parse, _ => 1L);
Console.WriteLine($"Parsing complete. ({timer.ElapsedMilliseconds}ms)");

timer.Restart();
Console.WriteLine($"Part 1: {CountStones(25, stones)} ({timer.ElapsedMilliseconds}ms)");

timer.Restart();
Console.WriteLine($"Part 2: {CountStones(75, stones)} ({timer.ElapsedMilliseconds}ms)");

return;

static long CountStones(int iterations, Dictionary<long, long> stones)
{
    for (var i = 0; i < iterations; i++)
    {
        var newStones = new Dictionary<long, long>();

        foreach (var (stone, count) in stones)
        {
            var length = Math.Floor(Math.Log10(stone) + 1);

            if (stone == 0)
            {
                AddStones(1, count);
            }
            else if (length % 2 == 0)
            {
                var left = (long)(stone / Math.Pow(10, length / 2));
                var right = (long)(stone % Math.Pow(10, length / 2));

                AddStones(left, count);
                AddStones(right, count);
            }
            else
            {
                AddStones(stone * 2024, count);
            }
        }

        stones = newStones;
        continue;

        void AddStones(long stone, long count)
        {
            newStones.TryAdd(stone, 0);
            newStones[stone] += count;
        }
    }

    return stones.Values.Sum();
}