private Estimate FindImpl(Game game, Estimate alpha, Estimate beta, int depth, int maxDepth, Metadata meta)
{
Player player = game.State.NextMovePlayer;
bool isMax = player == Player.Maximizing;
if (maxDepth - depth == 0)
{
return(game.State.StaticEstimate);
}
if (game.State.IsTerminate)
{
// make AI pick shortest path to terminate state
// otherwise there will be funny situation then AI seeing that it won
// w/o chances for other side will not purse the winning
Estimate terminateEstimate = game.State.StaticEstimate;
EstimateHelper.AdjustTerminalStateEstimate(depth, ref terminateEstimate);
return(terminateEstimate);
}
Estimate v = isMax
? Estimate.MinInf
: Estimate.MaxInf;
List <Move> moves = game.GetAllowedMoves()
.OrderByDescending(x => x.Priority)
.ToList();
foreach (Move move in moves)
{
meta.MovesChecked += 1;
using (DisposableMoveHandle.New(game, move))
{
Estimate curEstimate = FindImpl(game, alpha, beta, depth + 1, maxDepth, meta);
bool betterMoveFound = isMax
? curEstimate > v
: curEstimate < v;
if (betterMoveFound)
{
v = curEstimate;
if (depth == 1)
{
meta.BestMove = move;
}
}
if (isMax)
{
alpha = Estimate.Max(alpha, v);
}
else
{
beta = Estimate.Min(beta, v);
}
#if DEBUG
if (depth <= 3)
{
Trace.WriteLine($"{ new string(' ', depth) } - Move {move} for {player} -- {curEstimate} -- Term? {game.State.IsTerminate}");
}
#endif
if (alpha >= beta)
{
// alpha/beta cut-off
//Trace.WriteLine($"cut-off on depth {depth}");
break;
}
}
}
return(v);
}
