/*Score Tree using Alfa Beta pruning*/
void alfabeta(MinimaxNode *node, int a, int b, Color col) {
if (node->sons == NULL) {
if (node->depth%2==0) node->val = scoreBoard(node->game, col, node->depth);
else node->val = scoreBoard(node->game, oppositeCol(col), node->depth);
return;
}
if (node->depth % 2 == 0) {
int val = -ALFA_BETA_INFINITY;
int i;
for (i = 0; i < node->sonsK; i++) {
alfabeta(node->sons[i], a, b, oppositeCol(col));
val = maximum(val, node->sons[i]->val);
a = maximum(val, a);
if (b < a) break;
//if ((node->depth>2)&&(b <= a))break;
//if ((node->depth<=2) && (b < a))break;
}
node->val = val;
}
else {
int val = ALFA_BETA_INFINITY;
int i;
for (i = 0; i<node->sonsK; i++) {
alfabeta(node->sons[i], a, b, oppositeCol(col));
val = minimum(val, node->sons[i]->val);
b = minimum(val, b);
if (b < a) break;
//if ((node->depth>2) && (b <= a))break;
//if ((node->depth <= 2) && (b < a))break;
}
node->val = val;
}
}
int MoveEvaluater::alfabeta(int alfa, int beta, int depth, int who) {
if(depth >= maxdepth) {
return state.evaluate(who);
}
push();
Move m;
int v,e,p,r;
bool done = false;
for(v = alfa, p = state.firstMove(who,m); p >= 0 && !done; p = state.nextMove(who,m)) {
state.doMove(who, m);
if((e = -alfabeta(-beta,-v,depth+1, -who)) > v) {
v = e;
r = p;
}
if(v >= beta) {
done = true;
}
restore();
};
pop();
if(depth == 0 && v > bestscore) {
bestscore = v;
bestmove = r;
}
return v;
}
int MoveEvaluater::findmove(int who, int lookahead, const GameState &g) {
bestscore = MIN_SCORE;
bestmove = 0;
maxdepth = lookahead;
state = g;
stacktop = 0;
state.setEvaluate();
alfabeta(MIN_SCORE,MAX_SCORE,0, who);
return bestmove;
}
/*Build Minimax Tree according to Difficulty Level and Score Tree*/
MinimaxNode *getTree(Game *game, Color uCol) {
MinimaxNode *root = NULL;
if (game->difficulty < 5) {
root = getMinimaxTreeFixedDepth(game, 0, NULL, uCol);
}
else {
root = getMinimaxTreeBestDepth(game, uCol);
}
alfabeta(root, -ALFA_BETA_INFINITY, ALFA_BETA_INFINITY, uCol);
//printf("Root val is - %d\n", root->val);
return root;
}
