Solution Explanation for LeetCode Problem 2298: Tasks Count in the Weekend

This problem requires counting the number of tasks submitted on weekends (Saturday and Sunday) and weekdays from the Tasks table. The solution leverages the WEEKDAY() function in MySQL to efficiently achieve this.

Understanding WEEKDAY()

The WEEKDAY() function in MySQL returns an integer representing the day of the week, where 0 corresponds to Monday, 1 to Tuesday, ..., 5 to Saturday, and 6 to Sunday. This allows us to easily categorize days as weekdays or weekends based on their numerical representation.

MySQL Solution

SELECT
    SUM(WEEKDAY(submit_date) IN (5, 6)) AS weekend_cnt,
    SUM(WEEKDAY(submit_date) NOT IN (5, 6)) AS working_cnt
FROM Tasks;

This query efficiently computes the counts in a single pass through the Tasks table. Let's break it down:

• WEEKDAY(submit_date): This extracts the day of the week (as an integer from 0 to 6) for each submit_date.
• WEEKDAY(submit_date) IN (5, 6): This condition checks if the day of the week is either Saturday (5) or Sunday (6). It evaluates to 1 (true) for weekend days and 0 (false) for weekdays.
• SUM(WEEKDAY(submit_date) IN (5, 6)): This sums the results of the above condition. Since the condition is true only for weekend days, this sum directly represents the weekend_cnt.
• WEEKDAY(submit_date) NOT IN (5, 6): This is the negation of the weekend condition, identifying weekdays.
• SUM(WEEKDAY(submit_date) NOT IN (5, 6)): This sums the results, yielding the working_cnt.
• AS weekend_cnt, AS working_cnt: These aliases give meaningful names to the computed columns in the result set.

Time Complexity Analysis

The time complexity of this SQL query is O(N), where N is the number of rows in the Tasks table. The WEEKDAY() function operates on each row individually, and the SUM() function iterates through the results. Therefore, the query's runtime grows linearly with the table size.

Space Complexity Analysis

The space complexity is O(1), which is constant space. The query only stores a few intermediate variables (the counts for weekend and weekday tasks) regardless of the table size. The output is a small fixed-size result set.

No other programming languages are necessary because the problem is specifically about SQL database querying. The provided solution is already optimized for efficiency within the SQL context.