input: Write a function to find unique strings in a list.
  assert find_unique_strings(['apple', 'banana', 'apple', 'orange', 'banana']) == ['apple', 'banana', 'orange']
  assert find_unique_strings(['cat', 'dog', 'cat', 'mouse', 'dog', 'elephant']) == ['cat', 'dog', 'mouse', 'elephant']
  assert find_unique_strings(['a', 'b', 'c', 'a', 'b', 'd', 'e']) == ['a', 'b', 'c', 'd', 'e']
output: def find_unique_strings(strings):
      seen = set()
      unique = []
      for string in strings:
          if string not in seen:
              seen.add(string)
              unique.append(string)
      return unique