input: Write a python function to reverse a list and join its elements into a string.
  assert reverse_list([1, 3, 5, 7]) == '7531'
  assert reverse_list([10, 20, 30]) == '302010'
  assert reverse_list([4, 5, 6, 7, 8]) == '87654'
output: def reverse_list(lst):
      return ''.join(map(str, lst[::-1]))