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NegaMax help

Started by PacketLoss May 28, 2003 at 8:35 AM 1 replies 4k views

Original Post

May 28, 2003 at 8:35 AM

Hello again Ive implemented the negamax algorithm for my connect 4 game, but now i have a tiny problem. In my minimax aprouch to the problem i used the folowing "values" if player won return 100 if opponent won return -100 else return 0 Should i keep this or should i invert them, so that when the player wins the leaf returns -100?? Thx for your time. [edited by - PacketLoss on May 28, 2003 9:37:33 AM]

Russell

May 28, 2003 at 2:41 PM

In negamax, you return the score from the point of view of the side to move . So if the side to move has lost, then you would return -100, and if the side to move has won, you would return +100.

Russell

May 28, 2003 at 10:06 PM

Also, you should negate the score each time you return it. Here is an example, taken from this webpage:


int AlphaBeta(int depth, int alpha, int beta)
{
    if (depth == 0)
        return Evaluate();
    GenerateLegalMoves();
    while (MovesLeft()) {
        MakeNextMove();
        val = -AlphaBeta(depth - 1, -beta, -alpha); // <-- ***NEGATE HERE***
        UnmakeMove();
        if (val >= beta)
            return beta;
        if (val > alpha)
            alpha = val;
    }
    return alpha;
}

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