input: Write a function to reverse a string using dictionary and lambda function.
  assert reverseString("hello") == "olleh"
  assert reverseString("world") == "dlrow"
  assert reverseString("python") == "nohtyp"
output: def reverseString(s):
      return (lambda d: ''.join(d[i] for i in range(len(d)-1, -1, -1)))(dict(enumerate(s)))