int alpha_beta(game_state state, int depth, int alpha, int beta) {
if (alpha == beta) {
return alpha;
}
vector<pair<int, int> > children = state.get_all_no_tipping_moves();
if (depth == 0) {
return (int) children.size();
}
if (depth % 2 == 0) {
// get max, only alpha
// minimax 2(2,3), 1(0), 3(1,4,1)->first
for (int i = 0; i < children.size(); i ++) {
int value = alpha_beta(state.move_fast(children[i]), depth-1, alpha, beta);
if (value > alpha) {
alpha = value;
}
if (alpha >= beta) {
return alpha;
}
}
return alpha;
}
else {
// get min, only beta
// maxmini 2, 1, 3->second
for (int i = 0; i < children.size(); i ++) {
int value = alpha_beta(state.move_fast(children[i]), depth-1, alpha, beta);
if (value < beta) {
beta = value;
}
if (beta <= alpha) {
return beta;
}
}
return beta;
}
}
pair<int, int> ai_move(game_state state) {
vector<pair<int, int> > all_moves = state.get_all_no_tipping_moves();
if (all_moves.size() == 0) {
// if all moves would tip, surrender
return pair<int, int>(-1, 16);
}
// find best solution
int alpha = -1000;
int beta = 1000;
int best_index = 0;
if (state.game_turn < 15) {
ai_depth = 3;
}
else {
ai_depth = 4 + (state.game_turn-15) / 3;
}
cout << "[[TURN:" << state.game_turn << "]]\n";
cout << "======= depth: " << ai_depth << " ==========\n";
time_t s_time = time(NULL);
for (int ii = 0; ii < all_moves.size(); ii ++) {
int i = ii;
if (ai_depth % 2 == 0) {
i = (int) all_moves.size() - ii - 1;
}
int this_value = alpha_beta(state.move_fast(all_moves[i]), ai_depth-1, alpha, beta);
// cout << all_moves[i].first << "," << all_moves[i].second << " : " << this_value << "\n";
if (ai_depth % 2 == 0) {
// minimax 2(2,3), 1(0), 3(1,4,1)->first
if (this_value > alpha) {
alpha = this_value;
best_index = i;
}
}
else {
// maxmini 2,1,3->second
if (this_value < beta) {
beta = this_value;
best_index = i;
}
}
if (alpha >= beta) {
break;
}
}
time_t e_time = time(NULL);
cout << "======used: " << e_time-s_time << " seconds=======\n";
return all_moves[best_index];
}
