From 93800aeaab7389fc22628556b315dd5aae664416 Mon Sep 17 00:00:00 2001 From: TzeMingHo Date: Sun, 21 Jun 2026 16:57:23 +0100 Subject: [PATCH 1/4] completed common_prefix.py --- .../common_prefix/common_prefix.py | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/Sprint-2/improve_with_precomputing/common_prefix/common_prefix.py b/Sprint-2/improve_with_precomputing/common_prefix/common_prefix.py index f4839e7..3518a11 100644 --- a/Sprint-2/improve_with_precomputing/common_prefix/common_prefix.py +++ b/Sprint-2/improve_with_precomputing/common_prefix/common_prefix.py @@ -8,11 +8,11 @@ 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. """ 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 + sorted_strings = sorted(strings) + for string_index in range(len(sorted_strings) - 1): + common = find_common_prefix(sorted_strings[string_index], sorted_strings[string_index + 1]) + if len(common) > len(longest): + longest = common return longest From 4ca58a6d3db6c51df2ec2b1dc04f086331afae38 Mon Sep 17 00:00:00 2001 From: TzeMingHo Date: Sun, 21 Jun 2026 19:18:37 +0100 Subject: [PATCH 2/4] completed count_letters --- .../count_letters/count_letters.py | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/Sprint-2/improve_with_precomputing/count_letters/count_letters.py b/Sprint-2/improve_with_precomputing/count_letters/count_letters.py index 62c3ec0..e732e24 100644 --- a/Sprint-2/improve_with_precomputing/count_letters/count_letters.py +++ b/Sprint-2/improve_with_precomputing/count_letters/count_letters.py @@ -2,11 +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. """ + all_chars_set = set(s) + upper_set = set(letter for letter in all_chars_set if letter.isupper()) + lower_set = set(letter for letter in all_chars_set if letter.islower()) + only_upper = set() - for letter in s: - if is_upper_case(letter): - if letter.lower() not in s: - only_upper.add(letter) + for letter in upper_set: + if letter.lower() not in lower_set: + only_upper.add(letter) return len(only_upper) From 4b08e4cb19d8c3106ed69e7cd5c3127871281014 Mon Sep 17 00:00:00 2001 From: TzeMingHo Date: Tue, 23 Jun 2026 10:17:54 +0100 Subject: [PATCH 3/4] added big O comments --- .../improve_with_precomputing/common_prefix/common_prefix.py | 3 ++- .../improve_with_precomputing/count_letters/count_letters.py | 3 ++- 2 files changed, 4 insertions(+), 2 deletions(-) diff --git a/Sprint-2/improve_with_precomputing/common_prefix/common_prefix.py b/Sprint-2/improve_with_precomputing/common_prefix/common_prefix.py index 3518a11..57ab738 100644 --- a/Sprint-2/improve_with_precomputing/common_prefix/common_prefix.py +++ b/Sprint-2/improve_with_precomputing/common_prefix/common_prefix.py @@ -14,7 +14,8 @@ def find_longest_common_prefix(strings: List[str]): if len(common) > len(longest): longest = common return longest - +# before changes, it was N^2, bacause it got a for loop inside a for loop +# after changes, it is N + N. The first N for sorted, and another N for the loop. def find_common_prefix(left: str, right: str) -> str: min_length = min(len(left), len(right)) diff --git a/Sprint-2/improve_with_precomputing/count_letters/count_letters.py b/Sprint-2/improve_with_precomputing/count_letters/count_letters.py index e732e24..45e69e2 100644 --- a/Sprint-2/improve_with_precomputing/count_letters/count_letters.py +++ b/Sprint-2/improve_with_precomputing/count_letters/count_letters.py @@ -11,7 +11,8 @@ def count_letters(s: str) -> int: if letter.lower() not in lower_set: only_upper.add(letter) return len(only_upper) - +#before: it was N^2. It took a for loop and a not in s, which is a loop. +#after: it becomes N + N. The first N is the set created, it can access data instantly. The second N is the for loop. def is_upper_case(letter: str) -> bool: return letter == letter.upper() From 903ca2805098d4b0b8b5ced623f6eb84d95385b6 Mon Sep 17 00:00:00 2001 From: TzeMingHo Date: Tue, 23 Jun 2026 19:27:26 +0100 Subject: [PATCH 4/4] corrected big O for sorted in python --- .../improve_with_precomputing/common_prefix/common_prefix.py | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/Sprint-2/improve_with_precomputing/common_prefix/common_prefix.py b/Sprint-2/improve_with_precomputing/common_prefix/common_prefix.py index 57ab738..846d133 100644 --- a/Sprint-2/improve_with_precomputing/common_prefix/common_prefix.py +++ b/Sprint-2/improve_with_precomputing/common_prefix/common_prefix.py @@ -15,7 +15,7 @@ def find_longest_common_prefix(strings: List[str]): longest = common return longest # before changes, it was N^2, bacause it got a for loop inside a for loop -# after changes, it is N + N. The first N for sorted, and another N for the loop. +# after changes, it is NlogN + N. The NlogN is the worst case for sorted, and another N for the loop. def find_common_prefix(left: str, right: str) -> str: min_length = min(len(left), len(right))