gistfile1.rb

def valid_move_1?(scramble, move)
  if scramble.empty?
    true
  elsif same_face?(scramble[-1], move)
    false
  elsif scramble.count == 1
    true
  elsif same_axis?(scramble[-1], scramble[-2], move)
    false
  else
    true
  end
end

#####

def valid_move_2?(scramble, move)
  return true  if scramble.count == 0
  return false if same_face?(scramble[-1], move)
  return true  if scramble.count == 1
  return false if same_axis?(scramble[-1], scramble[-2], move)
  return true
end


#####

def valid_move_3?(scramble, move)
  !invalid_move?(scramble, move)
end

def invalid_move?(scramble, move)
  case scramble.count
  when 0
    false
  when 1
    same_face?(scramble[-1], move)
  else
    same_axis?(scramble[-1], scramble[-2], move) || same_face?(scramble[-1], move)
  end
end