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..fc6806d1 100644
--- a/Sprint-2/improve_with_precomputing/common_prefix/common_prefix.py
+++ b/Sprint-2/improve_with_precomputing/common_prefix/common_prefix.py
@@ -1,24 +1,26 @@
+
 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.
+    Return the longest prefix shared by any two strings.
+    Return an empty string if fewer than two strings are provided.
     """
+    if len(strings) < 2:
+        return ""
+
+    prefix_counts = {}
+
+    for string in strings:
+        for i in range(1, len(string) + 1):
+            prefix = string[:i]
+            prefix_counts[prefix] = prefix_counts.get(prefix, 0) + 1
+
     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
 
+    for prefix, count in prefix_counts.items():
+        if count >= 2 and len(prefix) > len(longest):
+            longest = prefix
 
-def find_common_prefix(left: str, right: str) -> str:
-    min_length = min(len(left), len(right))
-    for i in range(min_length):
-        if left[i] != right[i]:
-            return left[:i]
-    return left[:min_length]
+    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..66a60eb7 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.
+    Count uppercase letters that never appear in lowercase.
     """
-    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)
+    lowercase_letters = set()
+    uppercase_letters = set()
 
+    for letter in s:
+        if letter.islower():
+            lowercase_letters.add(letter)
+        elif letter.isupper():
+            uppercase_letters.add(letter)
 
-def is_upper_case(letter: str) -> bool:
-    return letter == letter.upper()
+    return sum(
+        1 for letter in uppercase_letters
+        if letter.lower() not in lowercase_letters
+    )