How do you solve Percentage of Users Attended a Contest on LeetCode?

Percentage of Users Attended a Contest (LeetCode #1633) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(n) time complexity and O(n) space complexity. Key insight: Using JOINs can significantly reduce the number of queries and improve performance.

What is the brute force solution for Percentage of Users Attended a Contest?

The brute force approach for Percentage of Users Attended a Contest is Brute Force, with O(n²) time complexity and O(1) space complexity. In the brute force approach, we will calculate the percentage of users registered for each contest by iterating through the Users and Register tables multiple times. This method is straightforward but inefficient for larger datasets. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Percentage of Users Attended a Contest?

Percentage of Users Attended a Contest uses the following concepts: Database. The recommended patterns to study are: Hash Map, Array.

What are the interview tips for Percentage of Users Attended a Contest?

Always clarify the requirements and constraints of the problem before diving into coding. Think about edge cases, such as no users or no registrations. Practice writing SQL queries on paper or in a text editor to get comfortable with syntax.

What are common mistakes when solving Percentage of Users Attended a Contest?

Not accounting for the total number of unique users correctly. Forgetting to round the percentage to two decimal places.

#1633

Percentage of Users Attended a Contest

Easy

DatabaseHash MapArray

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

	Brute Force	Optimal Solution★
Time	O(n²)	O(n)
Space	O(1)	O(n)

💡

Intuition

Time O(n)Space O(n)

In the optimal approach, we will use a single pass to gather the necessary counts, which allows us to efficiently compute the required percentages without redundant calculations.

⚙️

Algorithm

5 steps

1Step 1: Count the total number of unique users from the Users table.
2Step 2: Use a GROUP BY query on the Register table to count the number of unique users for each contest.
3Step 3: Calculate the percentage for each contest using the total user count.
4Step 4: Round the percentage to two decimal places.
5Step 5: Order the results by percentage in descending order and contest_id in ascending order.

solution.py7 lines

1# Full working Python code
2SELECT r.contest_id,
3       ROUND(COUNT(DISTINCT r.user_id) * 100.0 / total_users.total, 2) AS percentage
4FROM Register r
5JOIN (SELECT COUNT(DISTINCT user_id) AS total FROM Users) AS total_users ON 1=1
6GROUP BY r.contest_id
7ORDER BY percentage DESC, r.contest_id ASC;

ℹ

Complexity note: This complexity is due to the need to count unique users in both tables, but it is done in a single pass for the Register table and a single pass for the Users table.

1Using JOINs can significantly reduce the number of queries and improve performance.
2Understanding how to use GROUP BY effectively is crucial for aggregating data.

Solutions and explanations are original Tejav content. Problem titles © LeetCode — use the LeetCode button above for the full problem statement.