input: from typing import List
  
  
  def concatenate_strings(strings: List[str], separator: str) -> str:
      """
      Concatenate all elements in the list with the specified separator.
  
      >>> concatenate_strings(["Sample", "Text", "Hello"], "-")
      'Sample-Text-Hello'
      >>> concatenate_strings(["Sample", "Text", "Hello"], " ")
      'Sample Text Hello'
      >>> concatenate_strings([], "-")
      ''
      >>> concatenate_strings(["Single"], "-")
      'Single'
      """
output:     if not strings:
          return ""
      return separator.join(strings)