private EvalResult eval(
Board board,
int restDepth,
Turn currentTurn,
Evaluator evaluator,
double alpha,
double beta) {
if (restDepth == 0) return new EvalResult(evaluator.score(board, currentTurn), null);
// 置ける手を全て列挙
List<Position> puttablePositions = board.findPuttableHands(currentTurn.stone());
// 自分がおける場所がないならば、相手のターンになる。
if (puttablePositions.isEmpty()) {
double score =
-eval(board, restDepth - 1, currentTurn.flip(), evaluator, -beta, -alpha).getScore();
return new EvalResult(score, null);
}
if (restDepth >= 5) doMoveOrdering(board, puttablePositions, currentTurn, evaluator);
// 自分の番では、評価が最も大きくなるものを選ぶ。
double maxScore = Double.NEGATIVE_INFINITY;
Position selectedPosition = null;
for (Position p : puttablePositions) {
Board b = board.clone();
Evaluator e = evaluator.clone();
e.willPut(b, p.x, p.y, currentTurn.stone());
b.put(p.x, p.y, currentTurn.stone());
double a = Math.max(alpha, maxScore);
double score = -eval(b, restDepth - 1, currentTurn.flip(), e, -(a + 1), -a).getScore();
if (a < score && score < beta) {
e = evaluator.clone();
e.willPut(board, p.x, p.y, currentTurn.stone());
score = -eval(b, restDepth - 1, currentTurn.flip(), e, -beta, -score).getScore();
}
if (maxScore < score) {
maxScore = score;
selectedPosition = p;
}
// beta cut
if (maxScore >= beta) return new EvalResult(score, p);
}
assert (selectedPosition != null);
return new EvalResult(maxScore, selectedPosition);
}
protected List<Position> doMoveOrdering(
Board board, List<Position> ps, Turn currentTurn, Evaluator evaluator) {
List<EvalResult> shallowEvaluation = new ArrayList<EvalResult>();
for (Position p : ps) {
Board b = board.clone();
Evaluator e = evaluator.clone();
e.willPut(board, p.x, p.y, currentTurn.stone());
b.put(p.x, p.y, currentTurn.stone());
EvalResult er = eval(b, 2, currentTurn.flip(), e);
shallowEvaluation.add(new EvalResult(-er.getScore(), p));
}
// スコアの大きい方から並べる。
Collections.sort(shallowEvaluation, new HandComparator());
List<Position> result = new ArrayList<Position>();
for (EvalResult er : shallowEvaluation) result.add(er.getPosition());
return result;
}