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 f4839e70..2a373c4d 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 +1,25 @@
 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.
     """
+    # Pre-computation / Base-case optimization
+    if len(strings) < 2:
+        return ""
+
+    # Pre-computing step: Sort strings lexicographically.
+    # This groups strings with shared prefixes together so we only check adjacent pairs.
+    sorted_strings = sorted(strings)
+    
     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
+    for i in range(len(sorted_strings) - 1):
+        common = find_common_prefix(sorted_strings[i], sorted_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 62c3ec07..5cbfd87d 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 +1,18 @@
+
 def count_letters(s: str) -> int:
     """
-    count_letters returns the number of letters which only occur in upper case in the passed string.
+    Returns the number of letters which only occur in upper case
+    in the passed string.
     """
+    letters_present = set(s)
     only_upper = set()
-    for letter in s:
-        if is_upper_case(letter):
-            if letter.lower() not in s:
-                only_upper.add(letter)
+
+    for letter in letters_present:
+        if is_upper_case(letter) and letter.lower() not in letters_present:
+            only_upper.add(letter)
+
     return len(only_upper)
 
 
 def is_upper_case(letter: str) -> bool:
-    return letter == letter.upper()
+    return letter == letter.upper()
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