Class: Computer

Inherits:
Object
  • Object
show all
Defined in:
lib/ultimate_tic_tac_toe/computer.rb

Constant Summary collapse

HUMAN = 
"X"
COMPUTER = 
"O"
MAX_DEPTH =

to control length of calc time

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Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize ⇒ Computer

Returns a new instance of Computer.



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# File 'lib/ultimate_tic_tac_toe/computer.rb', line 9

def initialize
  @sub_alpha = []
  @best_move = 0
  @best_moves =[]
end

Instance Attribute Details

#active_player ⇒ Object

Returns the value of attribute active_player.



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# File 'lib/ultimate_tic_tac_toe/computer.rb', line 7

def active_player
  @active_player
end

#best_move ⇒ Object

Returns the value of attribute best_move.



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# File 'lib/ultimate_tic_tac_toe/computer.rb', line 7

def best_move
  @best_move
end

#sub_alpha ⇒ Object

Returns the value of attribute sub_alpha.



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# File 'lib/ultimate_tic_tac_toe/computer.rb', line 7

def sub_alpha
  @sub_alpha
end

Instance Method Details

#check_winner(board, depth) ⇒ Object 



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# File 'lib/ultimate_tic_tac_toe/computer.rb', line 39

def check_winner(board, depth)
  winner = 'None'
  winner = COMPUTER if board.winner?(COMPUTER)
  winner = HUMAN if board.winner?(HUMAN)
  winner = 'tie' if board.tie?
  winner = 'tie' if (depth >= MAX_DEPTH && board.grid.size > 10)
  winner
end

#computer_move(board) ⇒ Object 



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# File 'lib/ultimate_tic_tac_toe/computer.rb', line 15

def computer_move(board)
  if board.player_moves > board.computer_moves
    @active_player = COMPUTER
    computers_move(board)
  end
end

#computers_move(board) ⇒ Object 



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# File 'lib/ultimate_tic_tac_toe/computer.rb', line 22

def computers_move(board)
  if board.computer_moves < 0
    if board.unoccupied(6)
      board.store_position(6, COMPUTER)
    else
      board.store_position(8, COMPUTER)
    end
  else
    minimax(board, @active_player)
    board.store_position(@best_move, @active_player)
  end
end

#minimax(board, current_player) ⇒ Object 



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# File 'lib/ultimate_tic_tac_toe/computer.rb', line 35

def minimax(board, current_player)
  minimax_recurse(board, current_player, 0)
end

#minimax_recurse(board, player, depth) ⇒ Object 



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# File 'lib/ultimate_tic_tac_toe/computer.rb', line 49

def minimax_recurse(board, player, depth)
  winner = check_winner(board, depth)
  unless winner == 'None'
    if winner == 'tie'
      return 0
    elsif winner == @active_player
      return 1
    else
      return -1
    end
  end

  next_player = (player == COMPUTER ? HUMAN : COMPUTER )

  if player == @active_player
    alpha = -1
  else
    alpha = 1
  end

  possible_moves = board.get_move_list(board.grid)

  possible_moves.each do |move|
    new_board = board.dup
    new_board.grid = board.grid.dup
    next_board = new_board.simulate_move(new_board, move, player)
    @sub_alpha = minimax_recurse(next_board, next_player, depth + 1)

    if player == @active_player
      if ((depth == 0 ) && (alpha <= @sub_alpha ))
        @best_move = move
      end
      alpha = [alpha, @sub_alpha].max
    else
      alpha = [alpha, @sub_alpha].min
    end
  end
  alpha
end