input: Write a function that takes a list of strings and a separator/delimiter and returns the concatenation of all the elements with the specified separator. If the list is empty, return an empty string.
  def concatenate_strings(strings, separator):
   return separator.join(strings) if strings else ''
  assert concatenate_strings(["Sample","Text","Hello"], "-")=="Sample-Text-Hello"
  assert concatenate_strings(["Sample","Text","Hello"], ",")=="Sample,Text,Hello"
  assert concatenate_strings([], "-")==""
  assert concatenate_strings(["Sample"], "-")=="Sample"
  assert concatenate_strings(["Sample","Text"], "")=="SampleText"
output: def concatenate_strings(strings, separator):
   return separator.join(strings) if strings else ''