use precomputing for better performance

Author: aydaeslami

Sprint-2/improve_with_precomputing/common_prefix/common_prefix.py

@@ -7,12 +7,19 @@ 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 ""
+
+    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
+
+    for string_index in range(len(strings) - 1):
+        string = strings[string_index]
+        other_string = strings[string_index + 1]
+        common = find_common_prefix(string, other_string)
+        if len(common) > len(longest):
+            longest = common
+
     return longest
 
 
@@ -21,4 +28,4 @@ def find_common_prefix(left: str, right: str) -> str:
     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/count_letters/count_letters.py

@@ -1,14 +1,16 @@
 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()
+    upper_letters = set()
+    lower_letters = set()
+
     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.isupper():
+            upper_letters.add(letter)
+        elif letter.islower():
+            lower_letters.add(letter)
 
+    count = 0
+    for letter in upper_letters:
+        if letter.lower() not in lower_letters:
+            count += 1
 
-def is_upper_case(letter: str) -> bool:
-    return letter == letter.upper()
+    return count