ZA | 25-SDC-July | Faith Muzondo | Sprint 2 | improve with precomputing

Sprint-2/improve_with_precomputing/common_prefix/common_prefix.py

@@ -1,24 +1,31 @@
 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.
+    Returns the longest string common at the start of any two strings in the list.
     """
+    if len(strings) < 2:
+        return ""
+
+    # Precompute the set of prefixes for each string
+    prefixes = {}
+    for s in strings:
+        prefixes[s] = [s[:i] for i in range(1, len(s) + 1)]
+
     longest = ""
-    for string_index, string in enumerate(strings):
-        for other_string in strings[string_index+1:]:
-            common = find_common_prefix(string, other_string)
+    n = len(strings)
+    for i in range(n):
+        for j in range(i + 1, n):
+            # Compare prefixes of strings[i] and strings[j] efficiently
+            common = _common_prefix_precomputed(prefixes[strings[i]], strings[j])
             if len(common) > len(longest):
                 longest = common
-    return longest
 
+    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]
+def _common_prefix_precomputed(prefix_list: List[str], other: str) -> str:
+    # Find the longest prefix of other that exists in prefix_list
+    for prefix in reversed(prefix_list):
+        if other.startswith(prefix):
+            return prefix
+    return ""

Sprint-2/improve_with_precomputing/count_letters/count_letters.py

@@ -1,14 +1,11 @@
 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.
     """
-    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)
-
+    # Precompute sets of lowercase and uppercase letters in the string
+    lower_letters = {c for c in s if c.islower()}
+    upper_letters = {c for c in s if c.isupper()}
 
-def is_upper_case(letter: str) -> bool:
-    return letter == letter.upper()
+    # Count letters that appear only in uppercase
+    only_upper = {c for c in upper_letters if c.lower() not in lower_letters}
+    return len(only_upper)