Class: Reversi::Player::AlphaBetaAI

Inherits:
BasePlayer show all
Defined in:
lib/reversi/player/alpha_beta_ai.rb

Constant Summary collapse

N = 
10000.freeze

Instance Attribute Summary

Attributes inherited from BasePlayer

#board, #my_color, #opponent_color

Instance Method Summary collapse

Methods inherited from BasePlayer

#count_disks, #next_moves, #put_disk, #status

Constructor Details

#initialize(_color, _board) ⇒ AlphaBetaAI

Returns a new instance of AlphaBetaAI.



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# File 'lib/reversi/player/alpha_beta_ai.rb', line 6

def initialize(_color, _board)
  super

  points = [
    100, -10,  0, -1, -1,  0, -10, 100,
    -10, -30, -5, -5, -5, -5, -30, -10,
      0,  -5,  0, -1, -1,  0,  -5,   0,
     -1,  -5, -1, -1, -1, -1,  -5,  -1,
     -1,  -5, -1, -1, -1, -1,  -5,  -1,
      0,  -5,  0, -1, -1,  0,  -5,   0,
    -10, -30, -5, -5, -5, -5, -30, -10,
    100, -10,  0, -1, -1,  0, -10, 100
  ]
  @evaluation_value = 
    Hash[(1..8).map{ |x| (1..8).map{ |y| [[x, y], points.shift] } }.flatten(1) ]
end

Instance Method Details

#evaluate(move, board, alpha, beta, depth, color) ⇒ Object 



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# File 'lib/reversi/player/alpha_beta_ai.rb', line 33

def evaluate(move, board, alpha, beta, depth, color)
  put_disk(*move, color)
  moves = next_moves(!color)

  if depth == 1
    status[:mine].inject(0){ |sum, xy| sum + @evaluation_value[xy] }

  elsif moves.empty?
    case depth
    when ->(n){ n.odd? }  then alpha
    when ->(n){ n.even? } then beta end

  else
    case depth
    when ->(n){ n.odd? }
      beta = N
      moves.each do |move|
        val = evaluate(move, board, alpha, beta, depth - 1, !color)
        beta = val if val < beta
        return alpha if alpha > beta
      end
      beta
    when ->(n){ n.even? }
      alpha = -N
      moves.each do |move|
        val = evaluate(move, board, alpha, beta, depth - 1, !color)
        alpha = val if val > alpha
        return beta if alpha > beta
      end
      alpha
    end
  end

ensure
  board.undo!
end

#move(board) ⇒ Object 



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# File 'lib/reversi/player/alpha_beta_ai.rb', line 23

def move(board)
  moves = next_moves
  return if moves.empty?
  alpha = -N; beta = N
  next_move = moves.map do |move|
    { :move => move, :point => evaluate(move, board, alpha, beta, 3, true) }
  end.max_by{ |v| v[:point] }[:move]
  put_disk(*next_move)
end