Merge solver code with static interface

- Breaks backwards compat solver code with last version. Concurrent broke backwards compat because of race conditions with rng, but single is now broken too, despite it being 2x faster (!!!!)
- Literally twice as fast as Rust now in single thread
- Concurrent doesn't work yet, deadlocks somewhere..?

Benchmark/Program.cs

@@ -55,10 +55,10 @@ internal static class Program
         Debugger.Break();
         var s = Stopwatch.StartNew();
         if (true)
-            _ = Solver.Crafty.Solver.SearchStepwise(config, input, a => Console.WriteLine(a));
+            _ = SolverUtils.SearchStepwise<SolverSingle>(config, input, a => Console.WriteLine(a));
         else
         {
-            (var actions, _) = Solver.Crafty.Solver.SearchOneshot(config, input);
+            (var actions, _) = SolverUtils.SearchOneshot<SolverConcurrent>(config, input);
             foreach (var action in actions)
                 Console.Write($">{action.IntName()}");
             Console.WriteLine();

Craftimizer/Windows/SimulatorWindowSolver.cs

@@ -1,5 +1,6 @@
 using Craftimizer.Simulator;
 using Craftimizer.Simulator.Actions;
+using Craftimizer.Solver.Crafty;
 using Dalamud.Interface.Windowing;
 using System;
 using System.Collections.Concurrent;
@@ -71,7 +72,7 @@ public sealed partial class SimulatorWindow : Window, IDisposable
 
         SolverInitialActionCount = Actions.Count;
         SolverTaskToken = new();
-        SolverTask = Task.Run(() => Solver.Crafty.Solver.SearchStepwise(Service.Configuration.SolverConfig, solverState, SolverActionQueue.Enqueue, SolverTaskToken.Token));
+        SolverTask = Task.Run(() => SolverUtils.SearchStepwise<SolverConcurrent>(Service.Configuration.SolverConfig, solverState, SolverActionQueue.Enqueue, SolverTaskToken.Token));
     }
 
     public void Dispose()

Solver/Crafty/ActionSet.cs

@@ -17,11 +17,11 @@ public struct ActionSet
     private static ActionType ToAction(int index) => Simulator.AcceptedActions[index];
     [Pure]
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    private static uint ToMask(ActionType action) => 1u << (FromAction(action) + 1);
+    private static uint ToMask(ActionType action) => 1u << FromAction(action) + 1;
 
     // Return true if action was newly added and not there before.
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public bool AddAction(ActionType action)
+    public bool AddActionConcurrent(ActionType action)
     {
         var mask = ToMask(action);
         var old = Interlocked.Or(ref bits, mask);
@@ -30,13 +30,33 @@ public struct ActionSet
 
     // Return true if action was newly removed and not already gone.
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public bool RemoveAction(ActionType action)
+    public bool RemoveActionConcurrent(ActionType action)
     {
         var mask = ToMask(action);
         var old = Interlocked.And(ref bits, ~mask);
         return (old & mask) != 0;
     }
 
+    // Return true if action was newly added and not there before.
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public bool AddAction(ActionType action)
+    {
+        var mask = ToMask(action);
+        var old = bits;
+        bits |= mask;
+        return (old & mask) == 0;
+    }
+
+    // Return true if action was newly removed and not already gone.
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public bool RemoveAction(ActionType action)
+    {
+        var mask = ToMask(action);
+        var old = bits;
+        bits &= ~mask;
+        return (old & mask) != 0;
+    }
+
     [Pure]
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public readonly bool HasAction(ActionType action) => (bits & ToMask(action)) != 0;
@@ -51,10 +71,10 @@ public struct ActionSet
     public readonly bool IsEmpty => bits == 0;
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public readonly ActionType SelectRandom(Random random) => ElementAt(random.Next(Count));
+    public readonly ActionType SelectRandom(Random random) => ElementAt(0);// random.Next(Count));
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public ActionType? PopRandom(Random random)
+    public ActionType? PopRandomConcurrent(Random random)
     {
         uint snapshot;
         uint newValue;
@@ -76,7 +96,7 @@ public struct ActionSet
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public ActionType? PopFirst()
+    public ActionType? PopFirstConcurrent()
     {
         uint snapshot;
         uint newValue;
@@ -94,6 +114,23 @@ public struct ActionSet
         return action;
     }
 
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public ActionType PopRandom(Random random)
+    {
+        return PopFirst();
+        var action = ElementAt(random.Next(Count));
+        RemoveAction(action);
+        return action;
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public ActionType PopFirst()
+    {
+        var action = First();
+        RemoveAction(action);
+        return action;
+    }
+
     [Pure]
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public readonly ActionType First() => ElementAt(0);

Solver/Crafty/ArenaNode.cs

@@ -20,17 +20,17 @@ public sealed class ArenaNode<T> where T : struct
         private static int BatchCount = MaxSize / BatchSize;
 
         public ArenaNode<T>[][] Data;
-        private int index;
+        private int index; // Unused in single threaded workload
         private int count;
 
         public readonly int Count => count;
 
-        public void Add(ArenaNode<T> node)
+        public void AddConcurrent(ArenaNode<T> node)
         {
             if (Data == null)
                 Interlocked.CompareExchange(ref Data, new ArenaNode<T>[BatchCount][], null);
 
-            var idx = Interlocked.Increment(ref this.index) - 1;
+            var idx = Interlocked.Increment(ref index) - 1;
 
             var (arrayIdx, subIdx) = GetArrayIndex(idx);
 
@@ -42,6 +42,19 @@ public sealed class ArenaNode<T> where T : struct
             Interlocked.Increment(ref count);
         }
 
+        public void Add(ArenaNode<T> node)
+        {
+            Data ??= new ArenaNode<T>[BatchCount][];
+
+            var idx = count++;
+
+            var (arrayIdx, subIdx) = GetArrayIndex(idx);
+
+            Data[arrayIdx] ??= new ArenaNode<T>[BatchSize];
+
+            Data[arrayIdx][subIdx] = node;
+        }
+
         [Pure]
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         private static (int arrayIdx, int subIdx) GetArrayIndex(int idx) =>
@@ -59,6 +72,14 @@ public sealed class ArenaNode<T> where T : struct
         Parent = parent;
     }
 
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public ArenaNode<T> AddConcurrent(T state)
+    {
+        var node = new ArenaNode<T>(state, this);
+        Children.AddConcurrent(node);
+        return node;
+    }
+
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public ArenaNode<T> Add(T state)
     {

Solver/Crafty/ISolver.cs

@@ -0,0 +1,12 @@
+using Node = Craftimizer.Solver.Crafty.ArenaNode<Craftimizer.Solver.Crafty.SimulationNode>;
+
+namespace Craftimizer.Solver.Crafty;
+
+public interface ISolver
+{
+    abstract static void LoadChildData(Span<float> scoreSums, Span<int> visits, Span<float> maxScores, ref Node[] chunk, int iterCount);
+
+    abstract static bool SearchIter(ref SolverConfig config, Node rootNode, Random random, Simulator simulator);
+
+    abstract static void Search(ref SolverConfig config, Node rootNode, CancellationToken token);
+}

Solver/Crafty/NodeScores.cs

@@ -9,10 +9,17 @@ public struct NodeScores
     public float MaxScore;
     public int Visits;
 
-    public void Visit(float score)
+    public void VisitConcurrent(float score)
     {
         Intrinsics.CASAdd(ref ScoreSum, score);
         Intrinsics.CASMax(ref MaxScore, score);
         Interlocked.Increment(ref Visits);
     }
+
+    public void Visit(float score)
+    {
+        ScoreSum += score;
+        MaxScore = Math.Max(MaxScore, score);
+        Visits++;
+    }
 }

Solver/Crafty/SolverConcurrent.cs

@@ -0,0 +1,97 @@
+using System.Diagnostics.Contracts;
+using System.Runtime.CompilerServices;
+using Node = Craftimizer.Solver.Crafty.ArenaNode<Craftimizer.Solver.Crafty.SimulationNode>;
+
+namespace Craftimizer.Solver.Crafty;
+
+// https://github.com/alostsock/crafty/blob/cffbd0cad8bab3cef9f52a3e3d5da4f5e3781842/crafty/src/simulator.rs
+public sealed class SolverConcurrent : ISolver
+{
+    [MethodImpl(MethodImplOptions.AggressiveInlining | MethodImplOptions.AggressiveOptimization)]
+    public static void LoadChildData(Span<float> scoreSums, Span<int> visits, Span<float> maxScores, ref Node[] chunk, int iterCount)
+    {
+        for (var j = 0; j < iterCount; ++j)
+        {
+            var node = chunk[j]?.State.Scores ?? new();
+            scoreSums[j] = node.ScoreSum;
+            visits[j] = node.Visits;
+            maxScores[j] = node.MaxScore;
+        }
+    }
+
+    [Pure]
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static Node? EvalBestChild(ref SolverConfig config, int parentVisits, ref Node.ChildBuffer children) =>
+        parentVisits == 0 ?
+            null :
+            SolverUtils.EvalBestChild<SolverConcurrent>(ref config, parentVisits, ref children);
+
+    [Pure]
+    public static Node Select(ref SolverConfig config, Node rootNode)
+    {
+        var node = rootNode;
+        while (true)
+        {
+            var expandable = !node.State.AvailableActions.IsEmpty;
+            var likelyTerminal = node.Children.Count == 0;
+            if (expandable || likelyTerminal)
+                return node;
+
+            // select the node with the highest score
+            // if null (current node is invalid & not backpropagated just yet), try again from root
+            node = EvalBestChild(ref config, node.State.Scores.Visits, ref node.Children) ?? rootNode;
+        }
+    }
+
+    public static (Node ExpandedNode, float Score)? ExpandAndRollout(ref SolverConfig config, Node rootNode, Random random, Simulator simulator, Node initialNode)
+    {
+        ref var initialState = ref initialNode.State;
+        // expand once
+        if (initialState.IsComplete)
+            return (initialNode, initialState.CalculateScore(config.MaxStepCount) ?? 0);
+
+        var poppedAction = initialState.AvailableActions.PopRandomConcurrent(random);
+        if (!poppedAction.HasValue)
+            return null;
+        var expandedNode = initialNode.Add(SolverUtils.Execute(simulator, initialState.State, poppedAction.Value, true));
+
+        return SolverUtils.Rollout(ref config, rootNode, expandedNode, random, simulator);
+    }
+
+    public static void Backpropagate(Node rootNode, Node startNode, float score)
+    {
+        while (true)
+        {
+            startNode.State.Scores.VisitConcurrent(score);
+
+            if (startNode == rootNode)
+                break;
+
+            startNode = startNode.Parent!;
+        }
+    }
+
+    public static bool SearchIter(ref SolverConfig config, Node rootNode, Random random, Simulator simulator)
+    {
+        var selectedNode = Select(ref config, rootNode);
+        var rolledOut = ExpandAndRollout(ref config, rootNode, random, simulator, selectedNode);
+        if (!rolledOut.HasValue)
+            return false;
+
+        var (endNode, score) = rolledOut.Value;
+        Backpropagate(rootNode, endNode, score);
+        return true;
+    }
+
+    public static void SearchThread(SolverConfig config, Node rootNode, CancellationToken token) =>
+        SolverUtils.Search<SolverConcurrent>(ref config, rootNode, token);
+
+    public static void Search(ref SolverConfig config, Node rootNode, CancellationToken token)
+    {
+        var configP = config;
+        var tasks = new Task[config.ThreadCount];
+        for (var i = 0; i < config.ThreadCount; ++i)
+            tasks[i] = Task.Run(() => SearchThread(configP, rootNode, token), token);
+        Task.WaitAll(tasks, CancellationToken.None);
+    }
+}

Solver/Crafty/SolverSingle.cs

@@ -0,0 +1,79 @@
+using System.Diagnostics.Contracts;
+using System.Runtime.CompilerServices;
+using Node = Craftimizer.Solver.Crafty.ArenaNode<Craftimizer.Solver.Crafty.SimulationNode>;
+
+namespace Craftimizer.Solver.Crafty;
+
+// https://github.com/alostsock/crafty/blob/cffbd0cad8bab3cef9f52a3e3d5da4f5e3781842/crafty/src/simulator.rs
+public sealed class SolverSingle : ISolver
+{
+    [MethodImpl(MethodImplOptions.AggressiveInlining | MethodImplOptions.AggressiveOptimization)]
+    public static void LoadChildData(Span<float> scoreSums, Span<int> visits, Span<float> maxScores, ref Node[] chunk, int iterCount)
+    {
+        for (var j = 0; j < iterCount; ++j)
+        {
+            ref var node = ref chunk[j].State.Scores;
+            scoreSums[j] = node.ScoreSum;
+            visits[j] = node.Visits;
+            maxScores[j] = node.MaxScore;
+        }
+    }
+
+    [Pure]
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static Node EvalBestChild(ref SolverConfig config, int parentVisits, ref Node.ChildBuffer children) =>
+        SolverUtils.EvalBestChild<SolverSingle>(ref config, parentVisits, ref children);
+
+    [Pure]
+    public static Node Select(ref SolverConfig config, Node node)
+    {
+        while (true)
+        {
+            var expandable = !node.State.AvailableActions.IsEmpty;
+            var likelyTerminal = node.Children.Count == 0;
+            if (expandable || likelyTerminal)
+                return node;
+
+            // select the node with the highest score
+            node = EvalBestChild(ref config, node.State.Scores.Visits, ref node.Children);
+        }
+    }
+
+    public static (Node ExpandedNode, float Score) ExpandAndRollout(ref SolverConfig config, Node rootNode, Random random, Simulator simulator, Node initialNode)
+    {
+        ref var initialState = ref initialNode.State;
+        // expand once
+        if (initialState.IsComplete)
+            return (initialNode, initialState.CalculateScore(config.MaxStepCount) ?? 0);
+
+        var poppedAction = initialState.AvailableActions.PopRandom(random);
+        var expandedNode = initialNode.Add(SolverUtils.Execute(simulator, initialState.State, poppedAction, true));
+
+        return SolverUtils.Rollout(ref config, rootNode, expandedNode, random, simulator);
+    }
+
+    public static void Backpropagate(Node rootNode, Node startNode, float score)
+    {
+        while (true)
+        {
+            startNode.State.Scores.Visit(score);
+
+            if (startNode == rootNode)
+                break;
+
+            startNode = startNode.Parent!;
+        }
+    }
+
+    public static bool SearchIter(ref SolverConfig config, Node rootNode, Random random, Simulator simulator)
+    {
+        var selectedNode = Select(ref config, rootNode);
+        var (endNode, score) = ExpandAndRollout(ref config, rootNode, random, simulator, selectedNode);
+
+        Backpropagate(rootNode, endNode, score);
+        return true;
+    }
+
+    public static void Search(ref SolverConfig config, Node rootNode, CancellationToken token) =>
+        SolverUtils.Search<SolverSingle>(ref config, rootNode, token);
+}

Solver/Crafty/SolverUtils.cs

@@ -1,38 +1,14 @@
-using Craftimizer.Simulator;
 using Craftimizer.Simulator.Actions;
+using Craftimizer.Simulator;
+using Node = Craftimizer.Solver.Crafty.ArenaNode<Craftimizer.Solver.Crafty.SimulationNode>;
 using System.Diagnostics.Contracts;
 using System.Numerics;
 using System.Runtime.CompilerServices;
-using Node = Craftimizer.Solver.Crafty.ArenaNode<Craftimizer.Solver.Crafty.SimulationNode>;
 
 namespace Craftimizer.Solver.Crafty;
-
-// https://github.com/alostsock/crafty/blob/cffbd0cad8bab3cef9f52a3e3d5da4f5e3781842/crafty/src/simulator.rs
-public sealed class Solver
+public static class SolverUtils
 {
-    public SolverConfig Config;
-    public Node RootNode;
-
-    public Random Random;
-
-    public Solver(SolverConfig config, SimulationState state, bool strict)
-    {
-        Config = config;
-        var sim = new Simulator(state, config.MaxStepCount);
-        RootNode = new(new(
-            state,
-            null,
-            sim.CompletionState,
-            sim.AvailableActionsHeuristic(strict)
-        ));
-        Random = state.Input.Random;
-    }
-
-    public Solver(SolverConfig config, SimulationInput input, bool strict) : this(config, new SimulationState(input), strict)
-    {
-    }
-
-    private static SimulationNode Execute(Simulator simulator, SimulationState state, ActionType action, bool strict)
+    public static SimulationNode Execute(Simulator simulator, SimulationState state, ActionType action, bool strict)
     {
         (_, var newState) = simulator.Execute(state, action);
         return new(
@@ -53,7 +29,7 @@ public sealed class Solver
 
             if (!state.AvailableActions.HasAction(action))
                 return (startNode, CompletionState.InvalidAction);
-            state.AvailableActions.RemoveAction(action);
+            state.AvailableActions.RemoveActionConcurrent(action);
 
             startNode = startNode.Add(Execute(simulator, state.State, action, strict));
         }
@@ -63,7 +39,7 @@ public sealed class Solver
 
     [Pure]
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    private static Node ChildMaxScore(ref Node.ChildBuffer children)
+    public static Node ChildMaxScore(ref Node.ChildBuffer children)
     {
         var length = children.Count;
         var vecLength = Vector<float>.Count;
@@ -95,17 +71,29 @@ public sealed class Solver
     }
 
     [Pure]
-    [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    private Node? EvalBestChild(int parentVisits, ref Node.ChildBuffer children)
+    public static (List<ActionType> Actions, SimulationNode Node) Solution(Node node)
     {
-        if (parentVisits == 0)
-            return null;
+        var actions = new List<ActionType>();
+        while (node.Children.Count != 0)
+        {
+            node = ChildMaxScore(ref node.Children);
 
+            if (node.State.Action != null)
+                actions.Add(node.State.Action.Value);
+        }
+
+        return (actions, node.State);
+    }
+
+    [Pure]
+    [MethodImpl(MethodImplOptions.AggressiveInlining | MethodImplOptions.AggressiveOptimization)]
+    public static Node EvalBestChild<S>(ref SolverConfig config, int parentVisits, ref Node.ChildBuffer children) where S : ISolver
+    {
         var length = children.Count;
         var vecLength = Vector<float>.Count;
 
-        var C = MathF.Sqrt(Config.ExplorationConstant * MathF.Log(parentVisits));
-        var w = Config.MaxScoreWeightingConstant;
+        var C = MathF.Sqrt(config.ExplorationConstant * MathF.Log(parentVisits));
+        var w = config.MaxScoreWeightingConstant;
         var W = 1f - w;
         var CVector = new Vector<float>(C);
 
@@ -119,14 +107,7 @@ public sealed class Solver
         {
             var iterCount = Math.Min(vecLength, length);
 
-            ref var chunk = ref children.Data[i];
-            for (var j = 0; j < iterCount; ++j)
-            {
-                var node = chunk[j]?.State.Scores ?? new();
-                scoreSums[j] = node.ScoreSum;
-                visits[j] = node.Visits;
-                maxScores[j] = node.MaxScore;
-            }
+            S.LoadChildData(scoreSums, visits, maxScores, ref children.Data[i], iterCount);
 
             var s = new Vector<float>(scoreSums);
             var m = new Vector<float>(maxScores);
@@ -151,47 +132,21 @@ public sealed class Solver
         return children.Data[max.Item1][max.Item2];
     }
 
-    [Pure]
-    public Node Select()
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static (Node ExpandedNode, float Score) Rollout(ref SolverConfig config, Node rootNode, Node expandedNode, Random random, Simulator simulator)
     {
-        var node = RootNode;
-        while (true)
-        {
-            var expandable = !node.State.AvailableActions.IsEmpty;
-            var likelyTerminal = node.Children.Count == 0;
-            if (expandable || likelyTerminal)
-                return node;
-
-            // select the node with the highest score
-            // if null (current node is invalid & not backpropagated just yet), try again from root
-            node = EvalBestChild(node.State.Scores.Visits, ref node.Children) ?? RootNode;
-        }
-    }
-
-    public (Node ExpandedNode, float Score)? ExpandAndRollout(Simulator simulator, Node initialNode)
-    {
-        ref var initialState = ref initialNode.State;
-        // expand once
-        if (initialState.IsComplete)
-            return (initialNode, initialState.CalculateScore(Config.MaxStepCount) ?? 0);
-
-        var poppedAction = initialState.AvailableActions.PopRandom(Random);
-        if (!poppedAction.HasValue)
-            return null;
-        var expandedNode = initialNode.Add(Execute(simulator, initialState.State, poppedAction.Value, true));
-
         // playout to a terminal state
         var currentState = expandedNode.State.State;
         var currentCompletionState = expandedNode.State.SimulationCompletionState;
         var currentActions = expandedNode.State.AvailableActions;
 
         byte actionCount = 0;
-        Span<ActionType> actions = stackalloc ActionType[Config.MaxStepCount];
+        Span<ActionType> actions = stackalloc ActionType[config.MaxStepCount - currentState.ActionCount];
         while (true)
         {
             if (SimulationNode.GetCompletionState(currentCompletionState, currentActions) != CompletionState.Incomplete)
                 break;
-            var nextAction = currentActions.SelectRandom(Random);
+            var nextAction = currentActions.SelectRandom(random);
             actions[actionCount++] = nextAction;
             (_, currentState) = simulator.Execute(currentState, nextAction);
             currentCompletionState = simulator.CompletionState;
@@ -199,10 +154,10 @@ public sealed class Solver
         }
 
         // store the result if a max score was reached
-        var score = SimulationNode.CalculateScoreForState(currentState, currentCompletionState, Config.MaxStepCount) ?? 0;
+        var score = SimulationNode.CalculateScoreForState(currentState, currentCompletionState, config.MaxStepCount) ?? 0;
         if (currentCompletionState == CompletionState.ProgressComplete)
         {
-            if (score >= Config.ScoreStorageThreshold && score >= RootNode.State.Scores.MaxScore)
+            if (score >= config.ScoreStorageThreshold && score >= rootNode.State.Scores.MaxScore)
             {
                 (var terminalNode, _) = ExecuteActions(simulator, expandedNode, actions[..actionCount], true);
                 return (terminalNode, score);
@@ -211,80 +166,58 @@ public sealed class Solver
         return (expandedNode, score);
     }
 
-    public void Backpropagate(Node startNode, float score)
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static void Search<S>(ref SolverConfig config, Node rootNode, CancellationToken token) where S : ISolver
     {
-        while (true)
-        {
-            startNode.State.Scores.Visit(score);
-
-            if (startNode == RootNode)
-                break;
-
-            startNode = startNode.Parent!;
-        }
-    }
-
-    public void SearchThread(CancellationToken token)
-    {
-        Simulator simulator = new(RootNode.State.State, Config.MaxStepCount);
-        for (var i = 0; i < Config.Iterations; i++)
+        Simulator simulator = new(rootNode.State.State, config.MaxStepCount);
+        var random = rootNode.State.State.Input.Random;
+        for (var i = 0; i < config.Iterations; i++)
         {
             if (token.IsCancellationRequested)
                 break;
 
-            var selectedNode = Select();
-            var rolledOut = ExpandAndRollout(simulator, selectedNode);
-            if (!rolledOut.HasValue)
+            if (!S.SearchIter(ref config, rootNode, random, simulator))
             {
                 // Retry, count this iteration as moot
                 i--;
                 continue;
             }
-
-            var (endNode, score) = rolledOut.Value;
-            Backpropagate(endNode, score);
         }
     }
 
-    public void Search(CancellationToken token)
-    {
-        var tasks = new Task[Config.ThreadCount];
-        for (var i = 0; i < Config.ThreadCount; ++i)
-            tasks[i] = Task.Run(() => SearchThread(token), token);
-        Task.WaitAll(tasks, CancellationToken.None);
-    }
-
     [Pure]
-    public (List<ActionType> Actions, SimulationNode Node) Solution()
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static Node CreateRootNode(SolverConfig config, SimulationInput input, bool strict) =>
+        CreateRootNode(config, new SimulationState(input), strict);
+
+    [Pure]
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static Node CreateRootNode(SolverConfig config, SimulationState state, bool strict)
     {
-        var actions = new List<ActionType>();
-        var node = RootNode;
-        while (node.Children.Count != 0)
-        {
-            node = ChildMaxScore(ref node.Children);
-
-            if (node.State.Action != null)
-                actions.Add(node.State.Action.Value);
-        }
-
-        return (actions, node.State);
+        var sim = new Simulator(state, config.MaxStepCount);
+        return new(new(
+            state,
+            null,
+            sim.CompletionState,
+            sim.AvailableActionsHeuristic(strict)
+        ));
     }
 
-    public static (List<ActionType> Actions, SimulationState State) SearchStepwise(SolverConfig config, SimulationInput input, Action<ActionType>? actionCallback, CancellationToken token = default) =>
-        SearchStepwise(config, new SimulationState(input), actionCallback, token);
+    public static (List<ActionType> Actions, SimulationState State) SearchStepwise<S>(SolverConfig config, SimulationInput input, Action<ActionType>? actionCallback, CancellationToken token = default) where S : ISolver =>
+        SearchStepwise<S>(config, new SimulationState(input), actionCallback, token);
 
-    public static (List<ActionType> Actions, SimulationState State) SearchStepwise(SolverConfig config, SimulationState state, Action<ActionType>? actionCallback, CancellationToken token = default)
+    public static (List<ActionType> Actions, SimulationState State) SearchStepwise<S>(SolverConfig config, SimulationState state, Action<ActionType>? actionCallback, CancellationToken token = default) where S : ISolver
     {
         var actions = new List<ActionType>();
-        Simulator sim = new(state, config.MaxStepCount);
-        var solver = new Solver(config, state, true);
+        var sim = new Simulator(state, config.MaxStepCount);
+        var rootNode = CreateRootNode(config, state, true);
         while (!sim.IsComplete)
         {
             if (token.IsCancellationRequested)
                 break;
 
-            solver.Search(token);
-            var (solution_actions, solution_node) = solver.Solution();
+            S.Search(ref config, rootNode, token);
+            var (solution_actions, solution_node) = Solution(rootNode);
 
             if (solution_node.Scores.MaxScore >= 1.0)
             {
@@ -298,20 +231,20 @@ public sealed class Solver
 
             actionCallback?.Invoke(chosen_action);
 
-            solver = new Solver(config, state, true);
+            rootNode = CreateRootNode(config, state, true);
         }
 
         return (actions, state);
     }
 
-    public static (List<ActionType> Actions, SimulationState State) SearchOneshot(SolverConfig config, SimulationInput input, CancellationToken token = default) =>
-        SearchOneshot(config, new SimulationState(input), token);
+    public static (List<ActionType> Actions, SimulationState State) SearchOneshot<S>(SolverConfig config, SimulationInput input, CancellationToken token = default) where S : ISolver =>
+        SearchOneshot<S>(config, new SimulationState(input), token);
 
-    public static (List<ActionType> Actions, SimulationState State) SearchOneshot(SolverConfig config, SimulationState state, CancellationToken token = default)
+    public static (List<ActionType> Actions, SimulationState State) SearchOneshot<S>(SolverConfig config, SimulationState state, CancellationToken token = default) where S : ISolver
     {
-        var solver = new Solver(config, state, false);
-        solver.Search(token);
-        var (solution_actions, solution_node) = solver.Solution();
+        var rootNode = CreateRootNode(config, state, false);
+        S.Search(ref config, rootNode, token);
+        var (solution_actions, solution_node) = Solution(rootNode);
         return (solution_actions, solution_node.State);
     }
 }