Find maximum follow depth using recursion

You are given a directed follows relationship representing a social graph:

• Each record (follower_id, followee_id) means follower_id follows followee_id.
• Treat this as a directed graph.

Task

Implement a function that, given:

• a list of follow edges follows = [(follower_id, followee_id), ...]
• a starting user start_id

returns the maximum number of follow “layers” reachable from start_id by repeatedly following the next user.

Formally, compute the length of the longest directed path starting at start_id:

• Layer 1: users directly followed by start_id
• Layer 2: users followed by those users
• …

Return the maximum layer count reachable.

Requirements / edge cases

• Use recursion (you may add memoization).
• Handle cycles (e.g., A→B→C→A) without infinite recursion.
• If start_id follows nobody, return 0.

Example

If edges are: 1→2, 2→3, 3→4, then max_depth(1) = 3 (layers: {2}, {3}, {4}). If edges are: 1→2, 2→1, then max_depth(1) = 1 (cycle; do not loop forever).

Find Maximum Follow Depth with Recursion

You are given a directed social graph represented by follow relationships. Each record (follower_id, followee_id) means follower_id follows followee_id. Implement a function solution(follows, start_id) that returns the maximum number of follow layers reachable from start_id by repeatedly following users.

The depth is the number of directed edges in the longest path starting at start_id. A direct follow has depth 1.

Cycles must not cause infinite recursion. For this problem, a valid path may not visit the same user more than once. If a follow edge would lead to a user already in the current path, ignore that edge for that path.

If start_id follows nobody, return 0.

Constraints

• 0 <= len(follows) <= 200
• User IDs are integers and may be negative.
• At most 20 unique users are reachable from start_id.
• Duplicate follow edges may appear and should be treated as the same relationship.
• Cycles may exist in the graph.

Hints

1. Build an adjacency list from each follower to the users they directly follow.
2. Use recursive DFS with a visited set for the current path. If you memoize, the visited state must be part of the memoization key because cycles make the answer path-dependent.