def createVariableLists(variables):
  """Returns lists containing each of the common variables based on node type
  Args:
    variables: a dictionary of Var type variables
  Returns:
    wood, wheat, sheep, brick: lists of strings each representing nodes that are of the list's node type
  """
  wood, wheat, brick, sheep = [], [], [], []
  for key in variables:
    if "Wh" in key:
      wheat.append(key)
    elif "Wo" in key:
      wood.append(key)
    elif "Br" in key:
      brick.append(key)
    elif "Sh" in key:
      sheep.append(key)
  return wood, wheat, sheep, brick