AOC2021_06_2

readonly static string _puzzle = "06";
static List<int> _input = File.ReadAllText(Util.CurrentQuery.Location + $"\\{_puzzle}.txt").Split(',').Select(f => int.Parse(f)).ToList();
static int _targetDays = 256;

static ulong _lanternfishCount = 0;
static ulong _initialStateLanternfishCount = 0;

Dictionary<int, ulong> _initialStateLanternfish = new Dictionary<int, ulong>();
Dictionary<int, int> _initialStateCount = new Dictionary<int, int>();

void Main()
{
    //_input = File.ReadAllText(Util.CurrentQuery.Location + $"\\{_puzzle}_test.txt").Split(',').Select(f => int.Parse(f)).ToList();

    // calculate via divide and modulo how many fish are available after 80 days

    // for a set of fish, how many fish do they each create over _targetDays?
    // how many do that set create with their _targetDays?
    // This is a recursive function

    foreach (var i in _input)
    {
        // Oh, yeah, use a dictionary so we don't have to recalculate for each initial state in the input. /facepalm
        if (_initialStateLanternfish.ContainsKey(i))
        {
            _lanternfishCount += _initialStateLanternfish[i];
        }
        else
        {
            GenerateLanternfish(_targetDays, i);
            _initialStateLanternfishCount++;

            _lanternfishCount += _initialStateLanternfishCount;
            _initialStateLanternfish.Add(i, _initialStateLanternfishCount);
            _initialStateLanternfishCount = 0;
        }
    }

    //_lanternfish.Dump();

    _lanternfishCount.Dump();
    // 1639598111948
}

// Define other methods and classes here
void GenerateLanternfish(int targetDays, int initialState)
{
    for (var i = targetDays - initialState; i > 0; i -= 7)
    {
        GenerateLanternfish(i, 9);
        _initialStateLanternfishCount++;
    }
}