count_upper_letters

Author: Nataliia74

Sprint-2/improve_with_precomputing/count_letters/count_letters.py

@@ -1,13 +1,22 @@
-def count_letters(s: str) -> int:
+def count_letters(string: str) -> int:
     """
     count_letters returns the number of letters which only occur in upper case in the passed string.
     """
-    only_upper = set()
-    for letter in s:
-        if is_upper_case(letter):
-            if letter.lower() not in s:
-                only_upper.add(letter)
-    return len(only_upper)
+
+    lower_case_set = set()
+    upper_case_set = set()
+    
+    for letter in string:
+        if letter.islower():
+            lower_case_set.add(letter)
+        elif letter.isupper():
+            upper_case_set.add(letter)
+
+    count = 0
+    for letter in upper_case_set:
+       if letter.lower() not in lower_case_set:
+        count += 1
+    return count
 
 
 def is_upper_case(letter: str) -> bool: