Introduce option for HanabiState to save memory

include/game_state.h

@@ -62,6 +62,20 @@ namespace Hanabi
     std::array<inner_array_t, num_suits> _array{};
   };
 
+  struct HanabiStateConfig
+  {
+    /** What score to consider as a win. If left empty, automatically replaced by max score on construction. */
+    std::optional<uint8_t> score_goal;
+    /** The number of clues gained when a stack is finished or a card is discarded. Usually 1, 1/2 in clue starved. */
+    clue_t num_clues_gained_on_discard_or_stack_finished {1};
+    /**
+     * If set to true, only roughly half of the game states will be stored in the internal lookup table.
+     * This results in roughly halving memory consumption at the cost of roughly a factor 3-5 in execution speed
+     * (the slowdown is theoretically bounded to visiting at most 9 times the number of states if this option is activated).
+     * You should typically never need this, unless you are very specifically short on memory and.
+     * */
+    bool save_memory {false};
+  };
 
 // A game mimics a game state together with a list of actions and allows to traverse the game
 // history by making and reverting the stored actions.
@@ -71,7 +85,7 @@ namespace Hanabi
   public:
     HanabiState() = default;
 
-    explicit HanabiState(const std::vector<Card> & deck, uint8_t score_goal = 5 * num_suits, clue_t num_clues_gained_on_discard_or_stack_finished = 1);
+    explicit HanabiState(const std::vector<Card> & deck, HanabiStateConfig config = HanabiStateConfig());
 
     void give_clue() final;
 
@@ -263,10 +277,10 @@ namespace Hanabi
     RelativeRepresentationData _relative_representation;
 
     // Lookup table for states. Uses the ids calculated using the relative representation
+    bool const _save_memory;
     map_type<unsigned long, probability_t> _position_tablebase;
 
     std::uint64_t _enumerated_states{};
-
   };
 
   template<std::size_t num_suits, player_t num_players, std::size_t hand_size>

include/game_state.hpp

@@ -75,11 +75,11 @@ namespace Hanabi
   }
 
   template<suit_t num_suits, player_t num_players, hand_index_t hand_size>
-  HanabiState<num_suits, num_players, hand_size>::HanabiState(const std::vector<Card> & deck, uint8_t score_goal, clue_t num_clues_gained_on_discard_or_stack_finished):
+  HanabiState<num_suits, num_players, hand_size>::HanabiState(const std::vector<Card> & deck, HanabiStateConfig config):
-        _clues_gained_on_discard_or_stack_finished(num_clues_gained_on_discard_or_stack_finished)
+        _clues_gained_on_discard_or_stack_finished(config.num_clues_gained_on_discard_or_stack_finished)
-        , _score_goal(score_goal), _turn(0), _num_clues(max_num_clues), _num_strikes(0), _weighted_draw_pile_size(deck.size()), _stacks(), _hands(), _draw_pile()
+        , _score_goal(config.score_goal.value_or(num_suits * 5)), _turn(0), _num_clues(max_num_clues), _num_strikes(0), _weighted_draw_pile_size(deck.size()), _stacks(), _hands(), _draw_pile()
-        , _endgame_turns_left(no_endgame), _pace(deck.size() - score_goal - num_players * (hand_size - 1)), _score(0)
+        , _endgame_turns_left(no_endgame), _pace(deck.size() - _score_goal - num_players * (hand_size - 1)), _score(0)
-        , _actions_log(), _relative_representation(), _position_tablebase()
+        , _actions_log(), _relative_representation(), _save_memory(config.save_memory), _position_tablebase()
         , _enumerated_states(0)
   {
     std::fill(_stacks.begin(), _stacks.end(), starting_card_rank);
@@ -984,9 +984,15 @@ namespace Hanabi
 
   template<suit_t num_suits, player_t num_players, hand_index_t hand_size>
   bool HanabiState<num_suits, num_players, hand_size>::save_state_to_map()
+  {
+    if (_save_memory)
+    {
+      return _weighted_draw_pile_size % 2 == 0;
+    }
+    else
     {
       return true;
-    return _draw_pile.size() != 2;
+    }
   }
 
   template<suit_t num_suits, player_t num_players, hand_index_t hand_size>