feat(*): Add 2021-06 files (part 1 working, part 2 not)

2021/06/Program.cs

@@ -0,0 +1,61 @@
+namespace Day06
+{
+    class Program
+    {
+        static void Main(string[] args)
+        {
+            string input = File.ReadAllLines("input.txt")[0];
+            List<int> lanternFish = input.Split(',').Select(int.Parse).ToList();
+
+
+            //Part1(lanternFish);
+            Part2(lanternFish);
+        }
+
+        static void SimulateLanternFish(ref List<int> lanternFishPopulation, int daysToSimulate)
+        {
+            // A lanternfish that creates a new fish resets its timer to 6, not 7 (because 0 is included as a valid timer value). The new lanternfish starts with an internal timer of 8 and does not start counting down until the next day.
+
+            int currentDay = 1;
+
+            while (currentDay <= daysToSimulate)
+            {
+                Console.WriteLine($"Day: {currentDay} - there are {lanternFishPopulation.Count()} lantern fish");
+                for (int i = 0; i < lanternFishPopulation.Count; i++)
+                {
+                    switch(lanternFishPopulation[i]) 
+                    {
+                    case 0:
+                        // its internal timer would reset to 6, and it would create a new lanternfish with an internal timer of 8.
+                        lanternFishPopulation[i] = 6;
+                        // Adding a new one with 9 though it should be 8 as this loop will catch new fish and decrement them. It's dirty, but fast way to solve the issue
+                        lanternFishPopulation.Add(9);
+                        break;
+                    default:
+                        // remove one day from the fish's countdown
+                        lanternFishPopulation[i] -= 1;
+                        break;
+                    }
+                }
+
+                currentDay += 1;
+            }
+        }
+
+        static void Part1(List<int> lanternFish)
+        {
+            SimulateLanternFish(ref lanternFish, 80);
+
+            Console.WriteLine($"After 80 days there are {lanternFish.Count()} lantern fish.");
+        }
+
+        static void Part2(List<int> lanternFish)
+        {
+            SimulateLanternFish(ref lanternFish, 256);
+
+            // TODO - redo this using a database for large datasets, and entity framework, so as to avoid the HUGE memory usage
+            
+            Console.WriteLine($"After 256 days there are {lanternFish.Count()} lantern fish.");
+        }
+    }
+}