static float NegaScout(INode node, SearchConfig config, float alpha, float beta)
{
if (config.NodesSearched != null)
{
config.NodesSearched.Add(node);
}
if (node.IsGameOver || config.Depth == config.MaxDepth)
{
return(Sign[config.Colour] * node.Value);
}
ProcessNode(node, config.Depth, config.MaxDepth);
// Order children so NegaScout can search effectively
var orderedChildren = node.Children.OrderByDescending(x => x.Value);
var b = beta;
config.Colour = 1 - config.Colour;
config.Depth++;
var firstChildSearched = false;
foreach (var child in orderedChildren)
{
var t = -NegaScout(child, config, -b, -alpha);
if ((t > alpha) && (t < beta) && firstChildSearched)
{
t = -NegaScout(child, config, -beta, -alpha);
}
alpha = Math.Max(alpha, t);
if (alpha >= beta)
{
return(alpha);
}
b = alpha + 1;
firstChildSearched = true;
}
return(alpha);
}
static float AlphaBetaNegaMax(INode node, SearchConfig config, float alpha, float beta)
{
if (config.NodesSearched != null)
{
config.NodesSearched.Add(node);
}
if (node.IsGameOver || config.Depth == config.MaxDepth)
{
return(Sign[config.Colour] * node.Value);
}
ProcessNode(node, config.Depth, config.MaxDepth);
config.Colour = 1 - config.Colour;
config.Depth++;
var bestScore = Minimum;
foreach (var child in node.Children)
{
var gameState = child.GameState;
var score = GetScore(config.UseTranspositionTable, gameState) ?? -AlphaBetaNegaMax(child, config, -beta, -alpha);
AddHashToTranspositionTable(config.UseTranspositionTable, gameState, score);
if (score >= beta)
{
return(score);
}
if (score > bestScore)
{
bestScore = score;
}
if (score > alpha)
{
alpha = score;
}
}
return(bestScore);
}
public static float AlphaBetaNegaMax(INode node, SearchConfig config)
{
return(AlphaBetaNegaMax(node, config, -InitialAlphaBeta, InitialAlphaBeta));
}
public static float NegaScout(INode node, SearchConfig config)
{
return(NegaScout(node, config, -InitialAlphaBeta, InitialAlphaBeta));
}
public static float AlphaBetaNegaMax(INode node, SearchConfig config, IGameController gameController, Stopwatch searchTime = null)
{
return(AlphaBetaNegaMax(node, config, -InitialAlphaBeta, InitialAlphaBeta, gameController, searchTime));
}