diff --git a/Sprint-2/improve_with_precomputing/common_prefix/common_prefix.py b/Sprint-2/improve_with_precomputing/common_prefix/common_prefix.py
index f4839e7..b27e6b9 100644
--- a/Sprint-2/improve_with_precomputing/common_prefix/common_prefix.py
+++ b/Sprint-2/improve_with_precomputing/common_prefix/common_prefix.py
@@ -1,19 +1,20 @@
 from typing import List
 
-
-def find_longest_common_prefix(strings: List[str]):
+def find_longest_common_prefix(string_list: List[str]):
     """
     find_longest_common_prefix returns the longest string common at the start of any two strings in the passed list.
-
     In the event that an empty list, a list containing one string, or a list of strings with no common prefixes is passed, the empty string will be returned.
     """
-    longest = ""
-    for string_index, string in enumerate(strings):
-        for other_string in strings[string_index+1:]:
-            common = find_common_prefix(string, other_string)
-            if len(common) > len(longest):
-                longest = common
-    return longest
+    if len(string_list) < 2:
+        return ""
+    # Precompute: sort the strings so common prefixes are adjacent
+    sorted_strings = sorted(string_list)
+    longest_prefix = ""
+    for index in range(len(sorted_strings) - 1):
+        common_prefix = find_common_prefix(sorted_strings[index], sorted_strings[index + 1])
+        if len(common_prefix) > len(longest_prefix):
+            longest_prefix = common_prefix
+    return longest_prefix
 
 
 def find_common_prefix(left: str, right: str) -> str:
diff --git a/Sprint-2/improve_with_precomputing/count_letters/count_letters.py b/Sprint-2/improve_with_precomputing/count_letters/count_letters.py
index 62c3ec0..d3b3574 100644
--- a/Sprint-2/improve_with_precomputing/count_letters/count_letters.py
+++ b/Sprint-2/improve_with_precomputing/count_letters/count_letters.py
@@ -1,14 +1,14 @@
-def count_letters(s: str) -> int:
+def count_letters(text: 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)
+    # Find all lowercase letters in the string
+    lower_set = set(char for char in text if char.islower())
+    
+    # Find all uppercase letters in the string
+    upper_set = set(char for char in text if char.isupper())
+    
+    # Count uppercase letters that don't have lowercase versions
+    only_upper = {char for char in upper_set if char.lower() not in lower_set}
+    
     return len(only_upper)
-
-
-def is_upper_case(letter: str) -> bool:
-    return letter == letter.upper()