input: Write a function that concatenates a list of strings using a specified separator. If the list is empty, return an empty string.
  
  Input:
  
  concatenate_strings(["Sample", "Text", "Hello"], "-")
  
  Output:
  
  "Sample-Text-Hello"
  
  
  
  concatenate_strings([], "-")
  
  Output:
  
  ""
  
output: def concatenate_strings(strings, separator):
      if not strings:
          return ""
      return separator.join(strings)