/**
* Returns all the children of this node found so far. You probably won't
* want to call this method until you're sure you're done with getChild().
*
* @return <code>Node[]</code> of all known children for this node.
* @see getChild()
*/
public Node[] children() {
Node[] temp = new Node[this.childNum + 1];
for (int i = 0; i < this.childNum + 1; i++) {
temp[i] = this._children[i];
}
return temp;
}
/// <summary>
///
/// </summary>
/// <param name="n"></param>
/// <param name="min"></param>
/// <param name="a"></param>
/// <param name="b"></param>
/// <returns></returns>
private int minimaxAB( Node n, bool min, int a,int b) {
int alpha = a;
int beta = b;
if (n.isLeaf()) {
return n.value(this._player);
}
if (alpha > beta)
return min ? beta : alpha;
//Node child;
//
if (min) {
foreach (var child in n.Successors(null)){
int val = minimaxAB(child, false, alpha, beta);
if (val < beta) {
beta = val;
}
}
return beta;
} else {
foreach (var child in n.Successors(null)){
int val = minimaxAB(child, true, alpha, beta);
if (val > alpha) {
alpha = val;
}
}
return alpha;
}
}
// Implementation of mimimax with alpha-beta pruning.
private int minimaxAB( Node n, bool min, int a,
int b) {
int alpha = a;
int beta = b;
if (n.isLeaf()) {
return n.value(this._player);
}
Node child;
if (min) {
while (((child = n.getChild()) != null) && !(alpha > beta)) {
int val = minimaxAB(child, false, alpha, beta);
if (val < beta) {
beta = val;
}
}
return beta;
} else {
while (((child = n.getChild()) != null) && !(alpha > beta)) {
int val = minimaxAB(child, true, alpha, beta);
if (val > alpha) {
alpha = val;
}
}
return alpha;
}
}
/**
* Gets the next move of this player.
*
* @param board
* <code>Board</code> representation of the current game state.
* @param prev
* <code>Move</code> representing the previous move in the the
* game.
* @param color
* <code>int</code> representing the pieces this
* <code>Player</code> is playing with. One of
* <code>TicTacToe.NOUGHTS</code> or
* <code>TicTacToe.CROSSES</code>
* @return <code>Move</code> Next move of this player.
*/
public Move getMove( int[,] board, Move prev, int color) {
this._player = color;
Node root = new Node(board, prev);
int max = int.MinValue;
Node child;
Node bestNode = null;
while ((child = root.getChild()) != null) {
int val = minimaxAB(child, true, int.MinValue,
int.MaxValue);
if (val >= max) {
max = val;
bestNode = child;
}
}
return bestNode.move();
}
/// <summary>
/// Gets random successor
/// </summary>
/// <param name="heuristic"></param>
/// <returns></returns>
public IEnumerable<Node> Successors(Func<bool, int, int> heuristic)
{
Move[] moves = Board.GetEmptyPositions(_board, player());
moves = moves.Randomize();
int length = moves.Length;
for (int i = 0; i < length; i++)
{
int[,] newPos = Board.copy(_board);
Move move = moves[i];
Board.placePiece(newPos, move);
Node successor = new Node(newPos, move);
yield return successor;
}
}
/**
* Gets the "next" child for this node, or <code>null</code> if all
* children of this node have already been found.
*
* @return <code>Node</code> Representation of child (one move on) in the
* game tree.
*/
public Node getChild() {
bool firstColumn = true;
for (int x = this._x; x < 3; x++) {
int starter = 0;
if (firstColumn) {
starter = this._y;
}
for (int y = starter; y < 3; y++) {
Move m = new Move(x, y, this.player());
if (Board.isEmpty(this._board, m)) {
int[,] newPos = Board.copy(this._board);
Board.placePiece(newPos, m);
Node child = new Node(newPos, m);
this._children[this.childNum++] = child;
if (y >= (3 - 1)) {
this._x = (int) (x + 1);
this._y = 0;
} else {
this._x = x;
this._y = (int) (y + 1);
}
this._leaf = false;
this._leafdef = true;
return child;
}
}
firstColumn = false;
}
this._leaf = true;
this._leafdef = true;
return null;
}
