input: Write a function that takes a list of strings and a separator/delimiter as input and returns the concatenation of all the elements with the given separator. If the input list is empty, return an empty string.
  assert concatenate_strings(["Sample", "Text", "Hello"], "-") == "Sample-Text-Hello"
  assert concatenate_strings(["Sample", "Text", "Hello"], " ") == "Sample Text Hello"
  assert concatenate_strings(["Sample"], "-") == "Sample"
  assert concatenate_strings([], "-") == ""
output: def concatenate_strings(strings, separator):
      if not strings:
          return ""
      return separator.join(strings)