```python # a = "abc", nenu tuščias, unikalus (m) # s = "dfaga[bfkac]ebf" => "aceb" (n) O(n) # s = "cfaafb" => "cfaafb" # s = "affb" => "" from collections import Counter def min_s(a: str, s: str) -> str: need = Counter(a) ```