Leetcode #614: Second Degree Follower

In this guide, we solve Leetcode #614 Second Degree Follower in Python and focus on the core idea that makes the solution efficient.

You will see the intuition, the step-by-step method, and a clean Python implementation you can use in interviews.

Problem Statement

Table: Follow +-------------+---------+ | Column Name | Type | +-------------+---------+ | followee | varchar | | follower | varchar | +-------------+---------+ (followee, follower) is the primary key (combination of columns with unique values) for this table. Each row of this table indicates that the user follower follows the user followee on a social network.

Quick Facts

• Difficulty: Medium
• Premium: Yes
• Tags: Database

Intuition

The task is relational in nature, which maps cleanly to DataFrame operations in Python.

By treating tables as DataFrames, joins and group-bys become concise and readable.

Approach

Load the inputs as DataFrames and apply the appropriate merge, filter, or group-by.

Select or rename the columns to match the required output.

Steps:

• Load inputs as DataFrames.
• Apply merge/groupby/filter operations.
• Select the output columns.

Example

Python Solution

Complexity

The time complexity is O(n log n) (typical). The space complexity is O(n).

Edge Cases and Pitfalls

Watch for boundary values, empty inputs, and duplicate values where applicable. If the problem involves ordering or constraints, confirm the invariant is preserved at every step.

Summary

This Python solution focuses on the essential structure of the problem and keeps the implementation interview-friendly while meeting the constraints.