/** Returns the best move to make from here during a playout. */
short bestSearchMove(SearchNode node, McRunnable runnable) {
final Board runnableBoard = runnable.getBoard();
final MersenneTwisterFast random = runnable.getRandom();
short result = node.getWinningMove();
if (result != NO_POINT && runnableBoard.isLegal(result)) {
// The isLegal() check is necessary to avoid superko violations
return result;
}
float bestSearchValue = searchValue(node, PASS);
result = PASS;
final ShortSet vacantPoints = runnableBoard.getVacantPoints();
int start;
start = random.nextInt(vacantPoints.size());
int i = start;
final int skip = PRIMES[random.nextInt(PRIMES.length)];
do {
final short move = vacantPoints.get(i);
final float searchValue = searchValue(node, move);
if (searchValue > bestSearchValue) {
if (runnable.isFeasible(move) && runnableBoard.isLegal(move)) {
bestSearchValue = searchValue;
result = move;
} else {
node.exclude(move);
}
}
// Advancing by a random prime skips through the array
// in a manner analogous to double hashing.
i = (i + skip) % vacantPoints.size();
} while (i != start);
return result;
}
@Override
public short bestPlayMove() {
double mostWins = 1;
short result = PASS;
final ShortSet vacantPoints = board.getVacantPoints();
final SearchNode root = getRoot();
do {
mostWins = root.getWins(PASS);
// If the move chosen on the previous pass through this loop was
// illegal (e.g., because it was never actually tried in a playout),
// throw it out
if (result != PASS) {
log("Rejected " + board.getCoordinateSystem().toString(result) + " as illegal");
root.exclude(result);
result = PASS;
}
for (int i = 0; i < vacantPoints.size(); i++) {
final short move = vacantPoints.get(i);
if (root.getWins(move) > mostWins) {
mostWins = root.getWins(move);
result = move;
}
}
} while (result != PASS && !board.isLegal(result));
// Consider resigning
if (root.getWinRate(result) < RESIGN_PARAMETER) {
return RESIGN;
}
log(
"Selected "
+ board.getCoordinateSystem().toString(result)
+ " with "
+ root.getWins(result)
+ " wins in "
+ root.getRuns(result)
+ " runs");
return result;
}