West Midlands | 25-SDC-July | Gabriel Deng | Sprint 2 | Improve with precomputing

Sprint-2/improve_with_precomputing/common_prefix/common_prefix.py

@@ -7,18 +7,26 @@ def find_longest_common_prefix(strings: List[str]):
 
     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 not strings or len(strings) == 1:
+        return ""
+
     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
+
+    # Precompute: Build a dictionary of prefixes to their count
+    # For each string, generate all its prefixes and count occurrences
+    prefix_count = {}
+
+    for string in strings:
+        seen_prefixes = set()  # Avoid counting same prefix twice from same string
+        for i in range(len(string) + 1):
+            prefix = string[:i]
+            if prefix not in seen_prefixes:
+                prefix_count[prefix] = prefix_count.get(prefix, 0) + 1
+                seen_prefixes.add(prefix)
+
+    # Find the longest prefix that appears in at least 2 strings
+    for prefix, count in prefix_count.items():
+        if count >= 2 and len(prefix) > len(longest):
+            longest = prefix
+
     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]

Sprint-2/improve_with_precomputing/count_letters/count_letters.py

@@ -2,10 +2,14 @@ def count_letters(s: str) -> int:
     """
     count_letters returns the number of letters which only occur in upper case in the passed string.
     """
+    # Precompute: create set of all lowercase letters in the string (O(n))
+    lowercase_letters = set(c for c in s if c.islower())
+
+    # Now just count uppercase letters that don't have a lowercase version
     only_upper = set()
     for letter in s:
         if is_upper_case(letter):
-            if letter.lower() not in s:
+            if letter.lower() not in lowercase_letters:
                 only_upper.add(letter)
     return len(only_upper)