added code for the 2 exercises

Author: Luke-Manyamazi

Sprint-2/improve_with_precomputing/common_prefix/common_prefix.py

@@ -1,24 +1,29 @@
 from typing import List
 
-
 def find_longest_common_prefix(strings: 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.
     """
+    if len(strings) < 2:
+        return ""
+    
+    # Precompute by sorting - longest common prefixes will be between adjacent strings
+    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
+    
+    # Compare each string with its neighbor to find common prefixes
+    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
 
-
 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 left[:min_length]

Sprint-2/improve_with_precomputing/common_prefix/common_prefix_test.py

@@ -36,5 +36,32 @@ def test_really_long_list(self):
         common_prefix = find_longest_common_prefix(strings)
         self.assertRegex(common_prefix, "^hello.*$")
 
+    def test_multiple_equal_length_prefixes(self):
+        """Test when there are multiple prefixes of the same length"""
+        strings = [
+            "apple_pie",
+            "apple_cider", 
+            "banana_split",
+            "grape_bread",
+            "grape_pie"
+        ]
+        # Both "apple_" and "grape_" are length 6, either could be returned
+        result = find_longest_common_prefix(strings)
+        self.assertTrue(result in ["apple_", "grape_"])
+        self.assertEqual(len(result), 6)
+
+    def test_identical_strings(self):
+        """Test when multiple strings are identical"""
+        strings = [
+            "identical",
+            "different",
+            "identical", 
+            "identical",
+            "another"
+        ]
+        # The longest prefix is between identical strings: "identical"
+        self.assertEqual(find_longest_common_prefix(strings), "identical")
+
+
 if __name__ == "__main__":
     unittest.main()

Sprint-2/improve_with_precomputing/count_letters/count_letters.py

@@ -1,14 +1,25 @@
 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()
-    for letter in s:
-        if is_upper_case(letter):
-            if letter.lower() not in s:
-                only_upper.add(letter)
-    return len(only_upper)
-
-
-def is_upper_case(letter: str) -> bool:
-    return letter == letter.upper()
+    if not s:
+        return 0
+    
+    # Precompute using fixed arrays for maximum performance
+    has_upper = [False] * 26
+    has_lower = [False] * 26
+    
+    for char in s:
+        code = ord(char)
+        if 65 <= code <= 90:  # A-Z
+            has_upper[code - 65] = True
+        elif 97 <= code <= 122:  # a-z
+            has_lower[code - 97] = True
+    
+    # Count uppercase letters without lowercase counterparts
+    count = 0
+    for i in range(26):
+        if has_upper[i] and not has_lower[i]:
+            count += 1
+    
+    return count