optimized child generation

Author: gkcs

src/main/java/main/java/codingame/TicTacToe/TicTacToe.java

@@ -106,7 +106,14 @@ public int selectChild(final LargeBoard board) {
  double maxUtility = child.map(TreeNode::getUtility).orElse(0d);
  int bestColumn = child.map(c -> c.col).orElse(0);
  final Set<Integer> expandedSet = children.keySet();
- for (int i = 0; i < 81; i++) {
+ final int currentBoardIndex = board.currentBoard();
+ int max = 81;
+ int i = 0;
+ if (currentBoardIndex != -1) {
+ i = (currentBoardIndex / 3) * 27 + (currentBoardIndex % 3) * 3;
+ max = i + 21;
+ }
+ for (; i < max; i++) {
  if (board.canPlay(i) && !expandedSet.contains(i)) {
  final double utility = Math.sqrt(Math.log(plays + 1)) + (0.05 / Math.abs(9 / 2.0 - i));
  if (utility > maxUtility) {
@@ -126,9 +133,16 @@ private double simulate(final LargeBoard board, int player) {
  int numberOfMovesPlayed = board.movesPlayed;
  final int originalPlayer = player;
  while (board.result() == -1) {
- final int possibilities[] = new int[81];
+ final int currentBoardIndex = board.currentBoard();
+ int max = 81;
+ int position = 0;
+ if (currentBoardIndex != -1) {
+ position = (currentBoardIndex / 3) * 27 + (currentBoardIndex % 3) * 3;
+ max = position + 21;
+ }
+ final int possibilities[] = new int[max - position];
  int movesToPlay = 0;
- for (int position = 0; position < possibilities.length; position++) {
+ for (; position < max; position++) {
  if (board.canPlay(position)) {
  possibilities[movesToPlay] = position;
  movesToPlay++;
@@ -295,6 +309,17 @@ public boolean canPlay(final int p) {
  && (boards[bRow * 3 + bCol].occupied & (1 << (row * 3 + col))) == 0;
  }
 
+ public int currentBoard() {
+ if (movesPlayed > 0) {
+ final int previousMove = moves[movesPlayed - 1];
+ final int pMoveRow = (previousMove / 9) % 3, pMoveCol = previousMove % 3;
+ if ((largeOccupied & (1 << (pMoveRow * 3 + pMoveCol))) == 0) {
+ return pMoveRow * 3 + pMoveCol;
+ }
+ }
+ return -1;
+ }
+
  @Override
  public String toString() {
  return "LargeBoard{" +