gistfile1.rb

class TriangleClimber

  def initialize(size = nil, grid = nil)
    @possible_ways = 0
    @grid = grid ? grid.inject([]) {|r,e| r << e.strip.split(" ")}.reverse : nil
    @size = size || @grid.size
  end

  def find_possible_climbing_ways
    0.upto(@size - 1) {|x| move([0, x]) unless grid_has_trap?([0, x])}
    puts @possible_ways
  end

  private

  def move(from_point, to_point = nil)
    if to_point == [@size - 1, 0]
      @possible_ways += 1
    elsif to_point == nil
      (possible_moves(from_point)).each {|new_point| move(from_point, new_point) }
    else
      (possible_moves(to_point) - [from_point]).each {|new_point| move(to_point, new_point) }
    end
  end

  def possible_moves(point)
    x, y = point[0], point[1]
    [[x, y+1], [x, y-1], [x+1, y-1], [x+1, y]].reject {|x| disallowed_move?(x) }
  end

  def disallowed_move?(x)
    (x[0] + x[1] > @size - 1) || x[0] < 0 || x[1] < 0 || grid_has_trap?(x)
  end

  def grid_has_trap?(point)
    @grid && @grid[point[0]][point[1]].downcase == "x"
  end

end

TriangleClimber.new(4).find_possible_climbing_ways
TriangleClimber.new(nil,   [ "   O   ",
                             "  O O  ",
                             " O X O ",
                             "O O X O"]).find_possible_climbing_ways