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