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.
  assert concatenate_strings(["Sample", "Text", "Hello"], "|") == "Sample|Text|Hello"
  assert concatenate_strings(["Sample", "Text", "Hello"], ",") == "Sample,Text,Hello"
  assert concatenate_strings(["Hello"], " ") == "Hello"
  assert concatenate_strings([], "|") == ""
  assert concatenate_strings(["One", "Two"], "") == "OneTwo"
output: def concatenate_strings(strings, separator):
      if not strings:
          return ""
      return separator.join(strings)