// Return a numeric array for evaluation
// Self stone => +1.0, Opponent stone => -1.0, Blank => 0.0
int[,] GetBoardForEval(int color)
{
int[,] arr = new int[8, 8];
Array.Copy(board, arr, board.Length);
for (int i = 0; i < arr.GetLength(0); i++)
{
for (int j = 0; j < arr.GetLength(1); j++)
{
if (arr[i, j] == color)
{
arr[i, j] = 1;
}
else if (arr[i, j] == StoneColor.OppColor(color))
{
arr[i, j] = -1;
}
else
{
arr[i, j] = 0;
}
}
}
return(arr);
}
// Return the 2 dimentional array of the position where the stone is reversible
internal List <List <Pos> > GetReversibles(Pos pos, int color)
{
int[,] directionXY = new int[8, 2]
{
{ -1, -1 }, { 0, -1 }, { 1, -1 },
{ -1, 0 }, { 1, 0 },
{ -1, 1 }, { 0, 1 }, { 1, 1 }
};
List <List <Pos> > reversibleStones = new List <List <Pos> >();
for (int i = 0; i < directionXY.GetLength(0); i++)
{
reversibleStones.Add(new List <Pos>());
}
for (int i = 0; i < directionXY.GetLength(0); i++)
{
int dx = directionXY[i, 0];
int dy = directionXY[i, 1];
int x = pos.x;
int y = pos.y;
for (int j = 0; j < boardSize; j++)
{
x += dx;
y += dy;
if (!(0 <= x && x < boardSize && 0 <= y && y < boardSize))
{
reversibleStones[i] = new List <Pos>();
break;
}
if (board[y, x] == StoneColor.OppColor(color))
{
reversibleStones[i].Add(new Pos()
{
x = x, y = y
});
}
else if (board[y, x] == color)
{
break;
}
else
{
reversibleStones[i] = new List <Pos>();
break;
}
}
}
return(reversibleStones);
}
// Calculate evaluation value
internal double Evaluate(int color)
{
System.Random r = new System.Random();
double fs = (Confirms(color) - Confirms(StoneColor.OppColor(color)) + r.NextDouble() * 3) * 11;
double cn = (Availables(color).Count + r.NextDouble() * 2) * 10;
double bp = 0.0;
int[,] tmpBoard = GetBoardForEval(color);
for (int i = 0; i < boardSize; i++)
{
for (int j = 0; j < boardSize; j++)
{
bp += evaluateValue[i, j] * tmpBoard[i, j] * r.NextDouble() * 3;
}
}
return(w1 * bp + w2 * fs + w3 * cn);
}
// Alpha beta searching with transposition table
private double AlphaBeta(int[,] board, int color, int depth = 0, double alpha = double.NegativeInfinity, double beta = double.PositiveInfinity)
{
nodeCount += 1;
evaluator.SetBoard(board);
// Return evaluation value if reaching depth = depthMax or terminal node
if (depth >= currentDepthMax)
{
return(evaluator.Evaluate(selfColor));
}
// Return evaluation when game ends
List <Pos> newOptions = evaluator.Availables(color);
List <Pos> oppNewOptions = evaluator.Availables(StoneColor.OppColor(color));
if (newOptions.Count == 0 && oppNewOptions.Count == 0)
{
int selfStones = evaluator.CountStones(selfColor);
int oppStones = evaluator.CountStones(StoneColor.OppColor(selfColor));
if (selfStones > oppStones)
{
return(double.PositiveInfinity);
}
else if (selfStones < oppStones)
{
return(double.NegativeInfinity);
}
else
{
return(evaluator.Evaluate(selfColor));
}
}
// When only the opponent can put stone, go to next depth
if (newOptions.Count == 0)
{
depth += 1;
color = StoneColor.OppColor(color);
newOptions = oppNewOptions;
}
// Expand board and store the all child boards in children list
// Associate the child and the action of that time
List <int[, ]> children = new List <int[, ]>();
Dictionary <int[, ], Pos> actionChildTable = new Dictionary <int[, ], Pos>();
foreach (Pos action in newOptions)
{
Board childBoard = new Board();
childBoard.SetBoard(board);
childBoard.UpdateBoard(action, color);
children.Add(childBoard.GetBoard());
actionChildTable.Add(childBoard.GetBoard(), action);
}
// Sort children in order of the score
// In descending order when self turn and in ascending order when opponent turn
st.Start();
if (depth <= 3)
{
children = OrderBoards(children, color);
}
st.Stop();
// Alpha beta searching
if (color == selfColor)
{
// In self turn, search max value of children
double score = double.NegativeInfinity;
foreach (int[,] child in children)
{
// Check if the child is stored in transposition table and the node type is EXACT
// If it does, set the value for the score
// If not, start alpha-beta-searching in next depth and store the score
string childHash = BoardToHash(child);
if (transpositionTable.ContainsKey(childHash) && transpositionTable[childHash].Depth >= currentDepthMax && transpositionTable[childHash].NodeType == "EXACT")
{
transpositionCutCount += 1;
score = transpositionTable[childHash].Score;
}
else
{
score = AlphaBeta(child, StoneColor.OppColor(color), depth + 1, alpha, beta);
transpositionTable[childHash] = new TranspositionTableEntry(child, currentDepthMax, score);
}
if (score > alpha)
{
alpha = score;
// Get best action
if (depth == 0)
{
foreach (KeyValuePair <int[, ], Pos> kvp in actionChildTable)
{
if (kvp.Key.Cast <int>().SequenceEqual(child.Cast <int>()))
{
bestAction = kvp.Value;
}
}
}
}
// Beta cut
if (alpha >= beta)
{
betaCutCount += 1;
break;
}
}
return(alpha);
}
else
{
// If the opponent turn, search minimum value of children
double score = double.PositiveInfinity;
foreach (int[,] child in children)
{
string childHash = BoardToHash(child);
if (transpositionTable.ContainsKey(childHash) && transpositionTable[childHash].Depth >= currentDepthMax && transpositionTable[childHash].NodeType == "EXACT")
{
transpositionCutCount += 1;
score = transpositionTable[childHash].Score;
}
else
{
score = AlphaBeta(child, StoneColor.OppColor(color), depth + 1, alpha, beta);
transpositionTable[childHash] = new TranspositionTableEntry(child, currentDepthMax, score);
}
beta = Math.Min(beta, score);
// Alpha cut
if (beta <= alpha)
{
alphaCutCount += 1;
break;
}
}
return(beta);
}
}
void Reverse(Pos pos)
{
board[pos.y, pos.x] = StoneColor.OppColor(board[pos.y, pos.x]);
}