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    <p>Your alpha-beta code is probably wrong. Be aware of what happens when a player 'pass the turn' (i.e. has no available moves), i had a tricky bug in my code, due to this. </p> <p>Did you call the recursion with the alpha and beta values switched? Mine works like this (Java code):</p> <pre><code>private float minimax(OthelloBoard board, OthelloMove best, float alpha, float beta, int depth) { float bestResult = -Float.MAX_VALUE; OthelloMove garbage = new OthelloMove(); int state = board.getState(); int currentPlayer = board.getCurrentPlayer(); if (state == OthelloBoard.STATE_DRAW) return 0.0f; if ((state == OthelloBoard.STATE_BLACK_WINS) &amp;&amp; (currentPlayer == OthelloBoard.BLACK)) return INFINITY; if ((state == OthelloBoard.STATE_WHITE_WINS) &amp;&amp; (currentPlayer == OthelloBoard.WHITE)) return INFINITY; if ((state == OthelloBoard.STATE_BLACK_WINS) &amp;&amp; (currentPlayer == OthelloBoard.WHITE)) return -INFINITY; if ((state == OthelloBoard.STATE_WHITE_WINS) &amp;&amp; (currentPlayer == OthelloBoard.BLACK)) return -INFINITY; if (depth == maxDepth) return OthelloHeuristics.eval(currentPlayer, board); ArrayList&lt;OthelloMove&gt; moves = board.getAllMoves(currentPlayer); for (OthelloMove mv : moves) { board.makeMove(mv); alpha = - minimax(board, garbage, -beta, -alpha, depth + 1); board.undoMove(mv); if (beta &lt;= alpha) return alpha; if (alpha &gt; bestResult) { best.setFlipSquares(mv.getFlipSquares()); best.setIdx(mv.getIdx()); best.setPlayer(mv.getPlayer()); bestResult = alpha; } } return bestResult; } </code></pre> <p>The call is like:</p> <pre><code> OthelloMove bestFound = new OthelloMove(); int maxDepth = 8; minimax(board, bestFound, -Float.MAX_VALUE, Float.MAX_VALUE, maxDepth); //Wait for Thread to finish board.makeMove(bestFound); </code></pre> <p>Edit: In case a player has no available moves, getAllMoves() return a 'dummy move', that doesn't change the board at all, just pass the turn.</p> <p>Hope it helps!</p>
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