Day 21

Day20.cs

@@ -1,4 +1,4 @@
-#define Day20
+// #define Day20
 #if Day20
 using AoC2021;
 

Day21.cs

@@ -0,0 +1,116 @@
+#define Day21
+using System.Diagnostics;
+using System.Threading.Channels;
+using AoC2021;
+
+#if Day21
+
+var states = File.ReadAllLines("day21/input")
+    .Select(l => new State() {pos = int.Parse(l[l.Length-1].ToString()) - 1, score = 0})
+    .ToList();
+
+// states = new List<State>() {
+//     new State() {pos = 3, score = 0},
+//     new State() {pos = 7, score = 0},
+// };
+
+var states2 = states.Select(s => s.Copy()).ToList();
+
+var bla = Enumerable.Range(1, 3).SelectMany(x =>
+        Enumerable.Range(1, 3).SelectMany(y => Enumerable.Range(1, 3).Select(z => new {x = x, y = y, z = z})))
+    .Select(p => p.x + p.y + p.z).GroupBy(x => x).ToDictionary(x => x.Key, x => x.Count()); //ForEachAsList(p => Console.WriteLine(p));
+bla.ForEachAsList(b => Console.WriteLine($"{b.Key}: {b.Value}"));
+// System.Environment.Exit(0);
+
+int curPlayer = 0;
+int dieThrows = 0;
+int deterministic = 99;
+
+while (states[GetOtherPlayer(curPlayer)].score < 1000) {
+    dieThrows += 3;
+    var sumDie = GetDeterministic100Die().Take(3).Sum();
+    states[curPlayer].pos += sumDie;
+    states[curPlayer].pos %= 10;
+    states[curPlayer].score += states[curPlayer].pos + 1;
+    curPlayer = GetOtherPlayer(curPlayer);
+}
+
+var minScore = states.Select(s => s.score).Min();
+Console.WriteLine(minScore * dieThrows);
+
+
+//------------------
+
+Stopwatch sw = new Stopwatch();
+sw.Start();
+Stack<CompleteState> stack = new Stack<CompleteState>();
+stack.Push(new CompleteState(0, new StateRec(states2[0].pos, states2[0].score), new StateRec(states2[1].pos, states2[1].score), 1));
+
+long countWin0 = 0;
+long countWin1 = 0;
+
+while (stack.Count > 0) {
+    (int cur, StateRec p0, StateRec p1, long winTimes) = stack.Pop();
+    StateRec curP = cur == 0 ? p0 : p1;
+    AddState(Add(curP, 3), cur, p0, p1, winTimes * 1);
+    AddState(Add(curP, 4), cur, p0, p1, winTimes * 3);
+    AddState(Add(curP, 5), cur, p0, p1, winTimes * 6);
+    AddState(Add(curP, 6), cur, p0, p1, winTimes * 7);
+    AddState(Add(curP, 7), cur, p0, p1, winTimes * 6);
+    AddState(Add(curP, 8), cur, p0, p1, winTimes * 3);
+    AddState(Add(curP, 9), cur, p0, p1, winTimes * 1);
+}
+sw.Stop();
+Console.WriteLine(sw.Elapsed);
+Console.WriteLine(countWin0);
+Console.WriteLine(countWin1);
+
+
+StateRec Add(StateRec s, int die) {
+    int newPos = (s.pos + die) % 10;
+    return new StateRec(newPos, s.score + newPos + 1);
+}
+
+
+IEnumerable<int> GetDeterministic100Die() {
+    while (true) {
+        deterministic = (deterministic + 1) % 100;
+        yield return deterministic + 1;    
+    }
+}
+
+int GetOtherPlayer(int player) => player == 0 ? 1 : 0;
+
+void AddState(StateRec stateRec, int curPlayer, StateRec p0, StateRec p1, long winTimes) {
+    if (stateRec.score >= 21) {
+        if (curPlayer == 0) {
+            countWin0 += winTimes;
+        } else {
+            countWin1 += winTimes;
+        }
+    } else {
+        if (curPlayer == 0) {
+            stack.Push(new CompleteState(GetOtherPlayer(curPlayer), stateRec, p1, winTimes));
+        } else {
+            stack.Push(new CompleteState(GetOtherPlayer(curPlayer), p0, stateRec, winTimes));
+        }
+    }
+}
+
+class State {
+    public int pos { get; set; }
+    public int score { get; set; }
+
+    public State Copy() {
+        return new State() {pos = pos, score = score};
+    }
+
+    public override string ToString() {
+        return $"Pos: {pos}, Score: {score}";
+    }
+}
+
+record StateRec(int pos, int score);
+
+record CompleteState(int curPlayer, StateRec player0, StateRec player1, long winTimes);
+#endif

day21/input

@@ -0,0 +1,2 @@
+Player 1 starting position: 7
+Player 2 starting position: 8