// #define Day6
#if Day6
using System.Diagnostics;
var fish = File.ReadAllText("day6/input").Split(",")
    .Select(long.Parse)
    .GroupBy(x => x)
    .ToDictionary(x => x.Key, x => x.LongCount());

fish[0] = 0;
fish[6] = 0;
fish[7] = 0;
fish[8] = 0;

Console.WriteLine(CalculateGrowth(80, Copy(fish)));
Console.WriteLine(CalculateGrowth(256, Copy(fish)));

long CalculateGrowth(int numberOfDays, Dictionary<long, long> fishState) {
    while (numberOfDays > 0) {
        long newFish = fishState[0];
        for (int i = 0; i < 8; i++) {
            fishState[i] = fishState[i + 1];
        }
        fishState[6] += newFish;
        fishState[8] = newFish;

        numberOfDays--;
    }
    return fishState.Values.Sum();
}

Dictionary<long, long> Copy(Dictionary<long, long> dict) {
    return dict.ToDictionary(entry => entry.Key,
        entry => entry.Value);
}

// O(n)
long[] fishAsArray = fish.OrderBy(x => x.Key).Select(x => x.Value).ToArray();
int i = 0;
int days = 256;
int spawn = 6;
while (days > 0) {
    int newSpawn = (i + 7) % 9;
    fishAsArray[newSpawn] += fishAsArray[i];
    i = (i + 1) % 9;
    days--;
}
Console.WriteLine(fishAsArray.Sum());
#endif