Leetcode

Both LeetCode problems challenge you to manipulate data within a relational database using SQL. While seemingly similar, they focus on different aspects of data management: LeetCode 1683: Invalid Tweets deals with identifying and handling invalid data. You’ll write a query to find tweets with specific criteria that mark them as invalid. LeetCode 1378: Replace Employee ID With The Unique Identifier focuses on data transformation. Here, you’ll craft a query to replace existing employee IDs with a unique identifier within the database....

Challenges are often not a matter of difficulty, but of consistency. Yesterday I published two solutions for the first ‘LeetCode SQL 50’ challenge. To improve efficiency, I’ve decided to combine these solutions into one post for every 2 or 3 problems going forward. LeetCode 595 - Big Countries [SQL 3/50] This question introduces a new concept: double filtering. Together, we’ll learn how to use it effectively: A country is big if:...

As mentioned before, I’m tackling the LeetCode SQL challenge. This week’s problem, however, is surprisingly simple, making me wonder if it’s worth a dedicated write-up. Find the names of the customer that are not referred by the customer with id = 2. Return the result table in any order. The result format is in the following example. Example 1: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 Input: Customer table: +----+------+------------+ | id | name | referee_id | +----+------+------------+ | 1 | Will | null | | 2 | Jane | null | | 3 | Alex | 2 | | 4 | Bill | null | | 5 | Zack | 1 | | 6 | Mark | 2 | +----+------+------------+ Output: +------+ | name | +------+ | Will | | Jane | | Bill | | Zack | +------+ Solution To avoid repeating myself from the previous post (link above), I want to clarify that filtering for null values requires the IS NULL operator, not the equals sign (=)....

Leetcode has a Study Plan that focuses on solving SQL problems. The basic plan contains 50 problems, and when you finish them, you are awarded a cool badge. In between my many university assignments, I decided to take on this challenge as a goal, and of course, I’ll share my thoughts with you. The first problem in the challenge is: Write a solution to find the ids of products that are both low fat and recyclable....

On the first Leetcode question we need to achieve a target number by summing numbers from known list. We can solve this problem in two ways: brute force, which tries all combinations, or by using a dictionary for a more efficient lookup. Brute force - the easiest solution- but where’s the efficiency? I have a confession: most of the time, I prefer brute force code. It’s simpler and has a Soviet-era feel to it....

I recently started my master degree in data science with emphasis on machine learning, in order to training on my python skills I’m solving Leetcode challenges. In problem 709 we’re asking to replace every uppercase letter with the same lowercase letter. Basically, there’s two different ways to resolve this issue: Using The ‘Lower’ Method (the easiest solution) By using .lower we can convert every uppercase letter into lowercase: 1 2 3 class Solution: def toLowerCase(self, s: str) -> str: return s....