add selection

TP2/includes/mybt.h

@@ -101,7 +101,7 @@ struct bt_t {
   long long int mkH3();
 
   // MCTS
-  void mcts_selection(bt_node_t *);
+  bt_node_t *mcts_selection(bt_node_t *);
   void mcts_expansion(bt_node_t *);
   void mcts_simulation();
   void mcts_back_propagation();

TP2/src/mybt.cpp

@@ -193,7 +193,27 @@ bt_move_t bt_t::get_rand_move() {
   return moves[r];
 }
 
-void bt_t::mcts_selection(bt_node_t *node) { (void)node; }
+bt_node_t *bt_t::mcts_selection(bt_node_t *node) {
+  if (node->nb_simulation) {
+    bt_node_t *the_chosen = NULL;
+    float score = 0.;
+    for (auto i : node->children) {
+      // https://en.wikipedia.org/wiki/Monte_Carlo_tree_search#Exploration_and_exploitation
+      float curr_score =
+          static_cast<float>(i->wins) / i->nb_simulation +
+          sqrt(2) * sqrt(log(node->nb_simulation) / i->nb_simulation);
+      if (curr_score > score) {
+        the_chosen = i;
+        score = curr_score;
+      }
+    }
+    // Return the element with the higher score
+    return the_chosen;
+  } else {
+    // Return the first element if no simulation already done
+    return node->children[0];
+  }
+}
 
 void bt_t::mcts_expansion(bt_node_t *root) {
   update_moves();
@@ -234,15 +254,19 @@ bt_move_t bt_t::get_mcts_move(double max_time) {
   // MCTS
   while (elapsed.count() < max_time) {
     // Selection
+    auto xd = b_copy.mcts_selection(tree);
     std::cerr << "selection\n";
 
     // Expansion
+    // mcts_expansion(selected);
     std::cerr << "expansion\n";
 
     // Simulation
+    // bool is_win = mcts_simulation(selected);
     std::cerr << "simulation\n";
 
     // Update
+    // mcts_back_propagation(selected, is_win);
     std::cerr << "update\n";
 
     // Time constraint