How do you solve Find Followers Count on LeetCode?

Find Followers Count (LeetCode #1729) 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 GROUP BY and COUNT is much more efficient than manual counting.

What is the brute force solution for Find Followers Count?

The brute force approach for Find Followers Count is Brute Force, with O(n²) time complexity and O(1) space complexity. In the brute force approach, we will iterate through each user and count their followers by checking every entry in the Followers table. This 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 Find Followers Count?

Find Followers Count uses the following concepts: Database. The recommended patterns to study are: Hash Map, Array.

What are the interview tips for Find Followers Count?

Always clarify the requirements before diving into the solution. Practice writing SQL queries as they are common in data-related interviews. Be prepared to explain your thought process and the reasoning behind your approach.

What are common mistakes when solving Find Followers Count?

Not grouping results correctly, leading to incorrect counts. Forgetting to order results as specified in the problem.

#1729

Find Followers Count

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)

The optimal approach leverages SQL's GROUP BY and COUNT functions to efficiently aggregate the follower counts in a single query, which is much faster than the brute force method.

⚙️

Algorithm

4 steps

1Step 1: Use the SQL SELECT statement to choose user_id and count the number of follower_id for each user.
2Step 2: Use GROUP BY to group results by user_id to aggregate follower counts.
3Step 3: Order the results by user_id in ascending order.
4Step 4: Return the aggregated results.

solution.py5 lines

1# Full working Python code
2SELECT user_id, COUNT(follower_id) AS followers_count
3FROM Followers
4GROUP BY user_id
5ORDER BY user_id;

ℹ

Complexity note: The time complexity is O(n) because we are scanning through the table once to count followers. Space complexity is O(n) due to the storage of results.

1Using GROUP BY and COUNT is much more efficient than manual counting.
2Understanding how to leverage SQL functions can significantly reduce complexity.

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