input: Write a function to concatenate all elements of a list of strings with a specified separator. If the list is empty, the function should return an empty string.
  def concatenate_strings(strings, separator):
   return separator.join(strings)
  
  assert concatenate_strings(["Sample","Text","Hello"], " ") == "Sample Text Hello"
  assert concatenate_strings(["Sample","Text","Hello"], "-") == "Sample-Text-Hello"
  assert concatenate_strings([], ",") == ""
  assert concatenate_strings(["Single"], "-") == "Single"
  assert concatenate_strings(["First", "Second"], "/") == "First/Second"
output: def concatenate_strings(strings, separator):
   return separator.join(strings)