Which algorithms are available to solve Tic Tac Toe?

Question

What algorithms are available to solve Tic Tac Toe? Especially with board size 4 * 4 or bigger instead of 3 * 3? I tried 4 * 4 with Minimax & alpha-beta pruning but the pc seems to hang and throws exceptions on stack overflow. I saw these source code written in javascript but I don't know which algorithm it uses, could anyone clarify it for me? http://js-x.com/page/javascripts__example.html?view=153

Answer 1

try to do cut-offs in certain depth... i don't think you need more than 4 or 5 of depth to make a perfect move.

(java for 3*3 one-dim board with depth):

int minimax(int turn, int depth) { // turn(side to move) is 1 or -1
    int val = -turn; // worst value for that turn 
    int result = NULVAL;
    if (wins()) return turn; // evaluate board (board is a field)
    if (depth == 0) return DRAW;
    for (int i = 0; i < 9; i++) {
        if (board[i] == EMPTY) {
            board[i] = turn; // make move
            result = minimax(-turn, depth - 1);
            board[i] = EMPTY; // delete move
            if (result == turn) 
                return turn; // sees win
            if (result == DRAW)
                val = result;
        }
    }
    // if result keeps NULVAL: couldn't make a move (board is full)
    if (result == NULVAL) return DRAW;
    return val;
}