Refactor common_prefix and count_letter functions with precomputing.

Author: Emilianouz

Sprint-2/improve_with_precomputing/common_prefix/common_prefix.py

@@ -7,12 +7,17 @@ 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 len(strings) < 2:
+        return ""
+    # reducing comparison by sorting places strings with similar prefixes next to each other...
+    strings.sort()
+
     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(strings) - 1):
+        # compares only adjacent strings after sorting
+        common = find_common_prefix(strings[i], strings[i + 1])
+        if len(common) > len(longest):
+            longest = common
     return longest
 
 

Sprint-2/improve_with_precomputing/count_letters/count_letters.py

@@ -2,13 +2,23 @@ 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()
+    lower_case = set()
+    upper_case = set()
+
+    # collects lowercase and uppercase letters
     for letter in s:
-        if is_upper_case(letter):
-            if letter.lower() not in s:
-                only_upper.add(letter)
-    return len(only_upper)
+        if letter.islower():
+            lower_case.add(letter)
+        elif is_upper_case(letter):
+            upper_case.add(letter)
+
+    # counts uppercase letters not in lowercase
+    count = 0
+    for letter in upper_case:
+        if letter.lower() not in lower_case:
+            count += 1
 
+    return count
 
 def is_upper_case(letter: str) -> bool:
     return letter == letter.upper()