Class: TictactoeJ8th::AI

Inherits:
Object
  • Object
show all
Defined in:
lib/tictactoe_j8th/ai.rb

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(token) ⇒ AI

Returns a new instance of AI.



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# File 'lib/tictactoe_j8th/ai.rb', line 6

def initialize(token)
  @token = token
end

Instance Attribute Details

#token ⇒ Object (readonly)

Returns the value of attribute token.



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# File 'lib/tictactoe_j8th/ai.rb', line 4

def token
  @token
end

Instance Method Details

#move(board) ⇒ Object 



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# File 'lib/tictactoe_j8th/ai.rb', line 10

def move(board)
  return nil if board.full?

  # ####### Speed Hacks #######
  # Hacks to speed up minimax by bypassing most of the possible games.
  # The return statements here are important.  We make a move, then
  # bail out so that we don't end up analyzing all the possible games further down.
  # TODO:  See if there is a craftier, less hackish way to speed things up.

  # If the board is empty, always take the middle.
  if board.empty?
    board.place(token, 0)
    return 0
  end

  open_spots = get_open_spots(board)
  # If there is one spot taken, then always take the middle.
  # Unless the middle is taken already, then take the corner.
  if open_spots.count == Board::BOARD_SIZE-1
    spot = board[4].nil? ? 4 : 0
    board.place(token, spot)
    return spot
  end
  # ###### End Hacks ########


  enemy_token = discover_enemy_token(board)
  # Better here, but we do it above for our speed hacks.
  #open_spots = get_open_spots(board)
  games = Hash.new

  open_spots.each do |i|
    board_copy = board.create_copy
    board_copy.place(token, i)
    game = Game.new(board_copy, AI.new(enemy_token), AI.new(token))
    if game.winner == token
      board.place(token, i)
      return i
    end
    games[i] = game
  end

  scores = Hash.new

  games.each do |i, game|
    game.play
    scores[i] = 1 if game.winner == token
    scores[i] = -1 if game.winner == enemy_token
    scores[i] = 0 if game.winner.nil? and game.game_over?
  end

  max = scores.max_by { |k, v| v }
  spot = max[0]
  board.place(token, spot)
  spot
end