Use the post-order iterator in FindSubgameRoots

Author: d-kad

src/games/gametree.cc

@@ -1244,22 +1244,13 @@ std::map<GameInfosetRep *, GameNodeRep *> FindSubgameRoots(const Game &p_game)
   }
 
   SubgameScratchData data;
-  const int num_nodes = p_game->NumNodes();
 
-  // Collect nodes in ascending order (depth-first traversal) -- TODO: Replace with proper iterator
-  std::vector<GameNodeRep *> nodes_ascending;
-  nodes_ascending.reserve(num_nodes);
-  for (const auto &node : p_game->GetNodes()) {
-    nodes_ascending.push_back(node.get());
-  }
-
-  // Process in reverse order (descending node numbers, children before parents)
-  for (auto it = nodes_ascending.rbegin(); it != nodes_ascending.rend(); ++it) {
-    auto *node = *it;
+  // Process nodes in postorder
+  for (const auto &node : p_game->GetNodes(TraversalOrder::Postorder)) {
     if (node->IsTerminal() || data.dsu_parent.count(node->GetInfoset().get())) {
       continue;
     }
-    GenerateComponent(data, node);
+    GenerateComponent(data, node.get());
   }
 
   std::map<GameInfosetRep *, GameNodeRep *> result;

src/games/gametree.h

@@ -89,7 +89,7 @@ class GameTreeRep : public GameExplicitRep {
   /// Returns the largest payoff to the player in any play of the game
   Rational GetPlayerMaxPayoff(const GamePlayer &) const override;
   bool IsAbsentMinded(const GameInfoset &p_infoset) const override;
-  GameNode GetSubgameRoot(GameInfoset infoset) const override
+  GameNode GetSubgameRoot(const GameInfoset &infoset) const override
   {
     if (m_infosetSubgameRoot.empty()) {
       const_cast<GameTreeRep *>(this)->BuildSubgameRoots();