示例#1
0
      /// <summary>
      /// AlphaBeta Pruning algorithm adapted from genric AlphaBeta Pseudo-code: https://en.wikipedia.org/wiki/Alpha%E2%80%93beta_pruning
      /// </summary>
      /// <param name="game">Current game object (containing up-to-date board simulation)</param>
      /// <param name="alpha">Alpha value</param>
      /// <param name="beta">Beta value</param>
      /// <param name="maximizingPlayer">Maximizing player (True when it is THIS AI's turn in the simulation)</param>
      /// <returns></returns>
      private float AlphaBetaPrune(Game game, float alpha, float beta, bool maximizingPlayer)
      {
         // Check the current game state and if it is completed, return the (maximizing player's) value associated with the game outcome
         GameState state = game.GetGameState();

         if (state.IsCompleted)
         {
            if (state.Winner == this)
            {
               return 1f + (1f - state.TotalMoves / 9f);
            }
            else if (state.Winner == null)
            {
               return 0;
            }
            else
            {
               return -1f - (1f - state.TotalMoves / 9f); ;               
            }
         }

         // If the game was not completed by the previous move, continue recursing through possible moves
         float value;

         if (maximizingPlayer)
         {
            value = float.MinValue;

            foreach (Square square in game.Board.Squares)
            {
               if (square.Owner == null)
               {
                  square.Owner = this;
                  value = Math.Max(value, AlphaBetaPrune(game, alpha, beta, false));
                  alpha = Math.Max(alpha, value);
                  square.Owner = null;

                  if (beta <= alpha)
                  {
                     break;
                  }
               }               
            }
         }
         else
         {
            value = float.MaxValue;

            foreach (Square square in game.Board.Squares)
            {
               if (square.Owner == null)
               {
                  square.Owner = _playerOpponent;
                  value = Math.Min(value, AlphaBetaPrune(game, alpha, beta, true));
                  beta = Math.Min(beta, value);
                  square.Owner = null;

                  if (beta <= alpha)
                  {
                     break;
                  }
               }
            }
         }
         return value;
      }