Product catalog lookup: item attributes plus a cycle-safe tree of related items

A merchandise catalog is stored as a nested Python dictionary. Given an item, return that item's attributes, then follow its related items recursively and build the full tree of relationships rooted at the item. ```hint Settle the references first Before writing any recursion, decide how a related item is referenced and what your tree should contain when following references leads back to an item you are already expanding. ``` ### Clarifying Questions - How is a related item referenced: by an ID that has to be looked up elsewhere in the catalog, or nested inline under its parent? - Where do items sit in the nesting (for example under categories and subcategories), and can the same ID appear in two places? - Can relationships loop back (A relates to B and B relates to A), and how should a repeat appear in the tree? - What should happen when a related ID is missing from the catalog? ### What a Strong Answer Covers - Locating the item inside an arbitrarily nested structure, with a deliberate plan for lookups (index once versus search every time) - A recursive traversal that builds the tree in an explicitly defined output shape - Handling of cycles, items shared by several parents, missing references and malformed entries - Complexity, the recursion-depth limit, and an iterative alternative - Tests covering a leaf item, a shared related item, a cycle and a missing reference ### Follow-up Questions - The catalog grows to millions of items and the related-item chains get long. What breaks first in your solution, and what do you change? - Two related items both point to the same accessory. Should it appear twice in the tree or once, and how does each choice affect the output size? - How would you limit the tree to a maximum depth?