Find shortest relationship path using BFS

## Problem You are given a set of pairwise **relationships** between entities (people/services/etc.). Treat each relationship as an **undirected edge** in a graph. Given: - `relationships`: a list of pairs `[u, v]`, meaning `u` is related to `v`. - `start`: the starting entity. - `target`: the destination entity. ### Task 1. Build an adjacency structure (e.g., a hash map from node → neighbors). 2. Use **BFS** to find the **minimum number of relationship-hops** from `start` to `target`. ### Output Return the length of the shortest path in hops (number of edges). If `target` is unreachable, return `-1`. ### Follow-ups (discuss, no need to fully implement unless asked) - Return the actual path (list of nodes) instead of only its length. - Handle many queries (`start`, `target`) efficiently. - Consider directed relationships (only `u → v`). ### Constraints (reasonable assumptions) - `1 ≤ len(relationships) ≤ 2e5` - Node IDs are strings or integers. - Graph may be disconnected.