/// <summary>
/// Find the next node to play for the IA with the alpha beta algorithme
/// Based on the given pseudo code (IA course).
/// </summary>
/// <param name="node">The root node</param>
/// <param name="depth">The depth of the algorithm in the tree</param>
/// <param name="minOrMax">Maximize = 1, Minimize = -1</param>
/// <param name="parentVal">The parent value, first call +infinity to maximize, -infinity to minimize</param>
/// <returns>The winner node</returns>
private Tuple <float, Tuple <int, int> > AlphaBeta(IANode node, int depth, int minOrMax, bool whiteTurn, float parentVal = float.MaxValue)
{
// If depth 0 is reached or if the game is finished (TODO)
if (depth == 0 || node.Final())
{
return(new Tuple <float, Tuple <int, int> >(node.Eval(whiteTurn, minOrMax), new Tuple <int, int>(-1, -1)));
}
float currentVal = minOrMax * float.MinValue;
Tuple <int, int> currentMove = new Tuple <int, int>(-1, -1);
// Check for all possible move on the current board
foreach (Tuple <int, int> move in node.Moves)
{
// Apply the current move and create a new node with it
IANode newNode = node.Apply(move, whiteTurn);
// Recursiv call of AlphaBeta with changes
Tuple <float, Tuple <int, int> > res = AlphaBeta(newNode, depth - 1, -minOrMax, !whiteTurn, currentVal);
// Test if the new node of the parent node has a best value
if (res.Item1 * minOrMax > currentVal * minOrMax)
{
currentVal = res.Item1;
currentMove = new Tuple <int, int>(move.Item1, move.Item2);
if (currentVal * minOrMax > parentVal * minOrMax)
{
break;
}
}
}
return(new Tuple <float, Tuple <int, int> >(currentVal, currentMove));
}
/// <summary>
/// Applies the board state to this node and return the new node
/// </summary>
/// <param name="move">The move to apply to the board</param>
/// <returns>The new node if this board state</returns>
public IANode Apply(Tuple <int, int> move, bool whiteTurn)
{
Board board = LocalBoard.DeepCopyBoard();
bool isPlayable = board.IsPlayable(move.Item1, move.Item2, whiteTurn);
IANode node = null;
if (isPlayable)
{
board.PlayMove(move.Item1, move.Item2, whiteTurn);
node = new IANode(board, move, board.GetNextPossibleMoves(!whiteTurn));
}
return(node);
}
