Question

I’m generating a Tic-Tac-Toe game tree (9 seconds after the first move), and I’m told it should take only a few milliseconds. So I’m trying to optimize it, I ran it through CodeAnalyst and these are the top 5 calls being made (I used bitsets to represent the Tic-Tac-Toe board):

std::_Iterator_base::_Orphan_me

std::bitset<9>::test

std::_Iterator_base::_Adopt

std::bitset<9>::reference::operator bool

std::_Iterator_base::~_Iterator_base

void BuildTreeToDepth(Node &nNode, const int& nextPlayer, int depth)
{
   if (depth > 0)
   {
      //Calculate gameboard states
      int evalBoard = nNode.m_board.CalculateBoardState();
      bool isFinished = nNode.m_board.isFinished();
      if (isFinished || (nNode.m_board.isWinner() > 0))
      {
         nNode.m_winCount = evalBoard;
      }
      else
      {
         Ticboard tBoard = nNode.m_board;
         do
         {
            int validMove = tBoard.FirstValidMove();
            if (validMove != -1)
            {
               Node f;
               Ticboard tempBoard = nNode.m_board;
               tempBoard.Move(validMove, nextPlayer);
               tBoard.Move(validMove, nextPlayer);
               f.m_board = tempBoard;
               f.m_winCount = 0;
               f.m_Move = validMove;
               int currPlay = (nextPlayer == 1 ? 2 : 1);
               BuildTreeToDepth(f,currPlay, depth - 1);
               nNode.m_winCount += f.m_board.CalculateBoardState();
               nNode.m_branches.push_back(f);
            }
            else
            {
               break;
            }
         }while(true);
      }
   }
}

Where should I be looking to optimize it? How should I optimize these 5 calls (I don’t recognize them=.

Answer 1

The tic-tac-toe game tree is very redundant. Eliminating rotated and mirrored boards will reduce the final ply of the game tree by 3 or 4 orders of magnitude. No amount of optimizations will make bubblesort as fast as introsort.

struct Game_board;

struct Node
{
   Game_board game_board;
   Node* parent;
   std::vector<Node*> children;
   enum { X_Win, Y_Win, Draw, Playing } outcome;
};

// returns the same hash value for all "identical" boards.
// ie boards that can be rotated or mirrored to look the
// same will have the same hash value
int hash( const Game_board& game_board );

// uses hash() function to generate hashes from Node*
struct Hash_functor;

// nodes yet to be explored.
std::hash_set<Node*,Hash_functor> open;

//nodes already explored.
std::hash_set<Node*,Hash_functor> closed;

while( ! open.empty() )
{
   Node* node_to_expore = get_a_node( open );
   assert( node_to_expore not in close or open sets )
   if( node_to_expore is win lose or draw )
   {
      Mark node as win lose or draw
      add node to closed set
   }
   loop through all children of node_to_expore
   {
      if( child in close )
      {
         add node from closed set to children list of node_to_expore
      }
      else if( child in open )
      {
         add node from open set to children list of node_to_explore
      }
      else
      {
         add child to open set
         add child to children list of node_to_expore
      }
   }
}