count_letters

Author: craig-dsilva

Sprint-2/improve_with_precomputing/count_letters/count_letters.py

@@ -3,10 +3,10 @@ def count_letters(s: str) -> int:
     count_letters returns the number of letters which only occur in upper case in the passed string.
     """
     only_upper = set()
+    lowercase_letters = {letter for letter in s if not is_upper_case(letter)}
     for letter in s:
-        if is_upper_case(letter):
-            if letter.lower() not in s:
-                only_upper.add(letter)
+        if letter.lower() not in lowercase_letters:
+            only_upper.add(letter)
     return len(only_upper)