public (ulong move, int score) Solve(Position P, int depth)
{
var realDepth = Math.Min(depth, (Position.HEIGHT * Position.WIDTH - P.Moves));
if (realDepth < depth)
{
Console.WriteLine($"Search depth reduced to {realDepth}");
}
var color = P.PlayerToMove == Player.PlayerA ? 1 : -1;
var bestScore = Int32.MinValue;
ulong bestMove = 0;
var allMoves = P.GetMoves().ToList();
foreach (var move in allMoves)
{
Position p2 = new Position(P);
p2.Play(move);
var value = -Negamax(p2, realDepth - 1, Int32.MinValue, Int32.MaxValue, -color);
if (value > bestScore)
{
bestScore = value;
bestMove = move;
}
}
Console.WriteLine(bestScore);
return(bestMove, bestScore);
}
} // counter of explored nodes.
int Negamax(Position P, int depth, int alpha, int beta, int color)
{
if (P.ConnectedFour(P.CurrentPosition))
{
return(color * (1000 + EvaluateNode(P)));
}
if (P.Moves >= 42)
{
return(0);
}
if (depth == 0)
{
return(color * EvaluateNode(P));
}
NodeCount++;
int best = Int32.MinValue;
foreach (var move in P.GetMoves())
{
Position p2 = new Position(P);
p2.Play(move);
best = Math.Max(best, -Negamax(p2, depth - 1, -beta, -alpha, -color));
alpha = Math.Max(alpha, best);
if (alpha >= beta)
{
break; // prune the exploration if we find a possible move better than what we were looking for.
}
}
return(best);
}