//a straightforward implementation of the alpha-beta search, using iterative deepening search
public MoveResult AlphaBeta(CheckersBoard game, ref int maxDepth)
{
var iterativeDepth = _lastSuccessfulDepth;
const int alpha = NegativeInfinity;
const int beta = PositiveInfinity;
int totalNodesGenerated = 0, totalMaxPrunes = 0, totalMinPrunes = 0;
//limits itself to the difficulty level's max depth
AlphaBetaReturnValue lastCompletedMove = null;
while (iterativeDepth <= (int)_difficultyLevel)
{
ResetCounts();
maxDepth = 0;
var currentDepth = 0;
var copy = game.Clone();
var v = MaxValue(copy, alpha, beta, Color, ref currentDepth, ref maxDepth, iterativeDepth);
if (v != null)
{
lastCompletedMove = v;
Console.WriteLine(
"\tSearch at depth {0} completed. Optimal move found with value {1}; time to find move: {2}.\n" +
"\tNodes generated: {3}, max prunes: {4}, min prunes: {5}.\n",
maxDepth, lastCompletedMove.Value, DateTime.Now - AlphaBetaStartTime,
NodesGenerated, NumberOfMaxPrunes, NumberOfMinPrunes);
//keeps a running total of the total stats for the IDS
totalNodesGenerated += NodesGenerated;
totalMaxPrunes += NumberOfMaxPrunes;
totalMinPrunes += NumberOfMinPrunes;
}
else break;
if (maxDepth == 0 || !_depthCutoffHit || iterativeDepth == (int)_difficultyLevel)
break;
if(iterativeDepth != (int)_difficultyLevel)
iterativeDepth++;
}
_lastSuccessfulDepth = iterativeDepth;
Console.WriteLine(
"IDS ended. Optimal move found with value {0}; IDS stopped at depth {1}; time to find move: {2}.\n" +
"Total completed IDS stats: \n\tNodes generated: {3}. \n\tMax prunes: {4}. \n\tMin prunes: {5}.\n",
lastCompletedMove.Value, iterativeDepth, DateTime.Now - AlphaBetaStartTime,
totalNodesGenerated, totalMaxPrunes, totalMinPrunes);
return lastCompletedMove.Move;
}
