#
# Note 2.2.9
#
# Mon Mar 22 14:46:35 1999 -- Jens Svalgaard Frederiksen
#

from types import StringType, ListType

def reverseString(s):
  if s == "":
    return ""
  else:
    return reverseString(s[1:]) + s[0]


def reverseList(s):
  if s == []:
    return []
  else:
    return reverseList(s[1:]) + [s[0]]


def reverse(s):
  if type(s) == StringType:
    return reverseString(s)
  
  elif type(s) == ListType:
    return reverseList(s)

  else:
    return None


#
# Test
#

print reverse("kajak")      # kajak
print reverse("ost")        # tso
print reverse("")           # "" (tom streng)

print reverse([1,2,3])      # [3,2,1]
print reverse([])           # []