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..5e0832d 100644
--- a/Sprint-2/improve_with_precomputing/common_prefix/common_prefix.py
+++ b/Sprint-2/improve_with_precomputing/common_prefix/common_prefix.py
@@ -1,18 +1,27 @@
 from typing import List
 
 
-def find_longest_common_prefix(strings: List[str]):
+def find_longest_common_prefix(strings: List[str]) -> 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.
     """
+    # If the list has less than 2 strings, we can return early (nothing to compare)
+    if len(strings) < 2:
+        return ""
+    #Sort strings to bring similar ones next to each other
+    # This helps to find common parts faster without checking every possible pair!
+    strings.sort()
+    
     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
+   
+   #instead of checking all pairs (that is slow), just check each pair of neighbors
+    for i in range(len(strings) - 1):
+        common = find_common_prefix(strings[i], strings[i + 1])
+        if len(common) > len(longest):
+            longest = common
+
     return longest
 
 
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..a3203e9 100644
--- a/Sprint-2/improve_with_precomputing/count_letters/count_letters.py
+++ b/Sprint-2/improve_with_precomputing/count_letters/count_letters.py
@@ -2,11 +2,22 @@ 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()
+    # Store all lowercase and uppercase letters from the string
+    # This helps to check faster later
+    lower_letters = set()
+    upper_letters = set()
+    
+    # Go through the string once and fill the sets
     for letter in s:
         if is_upper_case(letter):
-            if letter.lower() not in s:
-                only_upper.add(letter)
+            upper_letters.add(letter)
+        else:
+            lower_letters.add(letter)
+   
+    # Only keep uppercase letters that don't have lowercase versions
+    # Using sets makes this check much faster
+    only_upper = {letter for letter in upper_letters if letter.lower() not in lower_letters}
+    
     return len(only_upper)