Day 6

Day5.cs

@@ -1,4 +1,4 @@
-#define Day5
+// #define Day5
 #define PartTwo
 #if Day5
 using System.Text.RegularExpressions;

Day6.cs

@@ -0,0 +1,34 @@
+#define Day6
+#if Day6
+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);
+}
+#endif

day6/input

@@ -0,0 +1 @@
+5,4,3,5,1,1,2,1,2,1,3,2,3,4,5,1,2,4,3,2,5,1,4,2,1,1,2,5,4,4,4,1,5,4,5,2,1,2,5,5,4,1,3,1,4,2,4,2,5,1,3,5,3,2,3,1,1,4,5,2,4,3,1,5,5,1,3,1,3,2,2,4,1,3,4,3,3,4,1,3,4,3,4,5,2,1,1,1,4,5,5,1,1,3,2,4,1,2,2,2,4,1,2,5,5,1,4,5,2,4,2,1,5,4,1,3,4,1,2,3,1,5,1,3,4,5,4,1,4,3,3,3,5,5,1,1,5,1,5,5,1,5,2,1,5,1,2,3,5,5,1,3,3,1,5,3,4,3,4,3,2,5,2,1,2,5,1,1,1,1,5,1,1,4,3,3,5,1,1,1,4,4,1,3,3,5,5,4,3,2,1,2,2,3,4,1,5,4,3,1,1,5,1,4,2,3,2,2,3,4,1,3,4,1,4,3,4,3,1,3,3,1,1,4,1,1,1,4,5,3,1,1,2,5,2,5,1,5,3,3,1,3,5,5,1,5,4,3,1,5,1,1,5,5,1,1,2,5,5,5,1,1,3,2,2,3,4,5,5,2,5,4,2,1,5,1,4,4,5,4,4,1,2,1,1,2,3,5,5,1,3,1,4,2,3,3,1,4,1,1