OA — Recipe Manager (4-Level CodeSignal)

Recent OA variant. CodeSignal, 90 minutes, 4 levels. CRUD on recipes (case-insensitive names), sorting by ingredient count, attaching a user model with edit permissions, and a version-history layer with rollback. Requirements Level 1 — CRUD def add_recipe(self, recipe_id: str, name: str, ingredients: list[str]) -> bool: ... # True on creation. False if recipe_id is taken OR if `name` (case-insensitive) # is already used by any recipe. Store `name` verbatim — only the lookup is lower-cased. def get_recipe(self, recipe_id: str) -> dict | None: ... # Returns {"id": ..., "name": ..., "ingredients": [...]} for the current version, # or None if missing. def update_recipe(self, recipe_id: str, name: str, ingredients: list[str]) -> bool: ... # Updates name + ingredients. False if recipe missing OR if the new name # (case-insensitive) belongs to a *different* recipe. A recipe can keep its # own name on update — collision check excludes self. def delete_recipe(self, recipe_id: str) -> bool: ... # True if deleted; False if missing. Level 2 — Search & sort def search_recipes(self, query: str) -> list[dict]: ... # Substring match on name, case-insensitive. # Sort: len(ingredients) asc, then recipe_id asc (numeric if all-digits, else lexicographic). def get_all_recipes(self) -> list[dict]: ... # Same sort as search_recipes; empty list if empty store. Level 3 — User system def add_user(self, user_id: str, username: str) -> bool: ... # True on creation; False if user_id is taken. def edit_recipe(self, user_id: str, recipe_id: str, name: str, ingredients: list[str]) -> bool: ... # Replaces Level-1 update_recipe semantics with a user check. # False if user_id is invalid, recipe is missing, or the new name belongs # to a different recipe (case-insensitive, self excluded). # Some variants additionally require the user to own / be permitted on # the recipe — confirm against the visible sample tests. Level 4 — Versioning + rollback edit_recipe and update_recipe no longer overwrite; each call appends a new version to the recipe's history list. Versions are numbered 1-based, never reset, never reused. def get_recipe_history(self, recipe_id: str) -> list[dict] | None: ... # Returns [{"version": 1, "name": ..., "ingredients": [...]}, ...] oldest first. # None if the recipe is missing. def rollback_recipe(self, user_id: str, recipe_id: str, version: int) -> bool: ... # Appends a copy of history[version - 1] as the NEW newest version. # Does NOT truncate or delete history. # False if user invalid, recipe missing, version out of range, # OR if the old name (at that version) is now used by a *different* current recipe. # A recipe never conflicts with its own earlier versions. Examples # History after add + edit + edit + rollback to v1 add_recipe("r1", "Pasta", ["egg", "flour"]) # v1 = "Pasta" edit_recipe("u1", "r1", "Spaghetti", ["egg", "flour"]) # v2 = "Spaghetti" edit_recipe("u1", "r1", "Carbonara", ["egg", "pork"]) # v3 = "Carbonara" rollback_recipe("u1", "r1", 1) # v4 = "Pasta" (copy of v1) # get_recipe_history("r1") → versions 1..4 with names Pasta, Spaghetti, Carbonara, Pasta Notes 90-minute hard cap. Candidates routinely complete 3 of 4 levels — finishing L1–L3 cleanly is more valuable than a buggy L4. Case-insensitivity is enforced everywhere — apply lower-cased comparison uniformly in add_recipe, update_recipe, edit_recipe, search_recipes, AND the rollback collision check. One Recipe dataclass with a versions: list[RecipeVersion] field collapses both edit and rollback into versions.append(...). Maintain a separate name_lower → recipe_id map for the O(1) uniqueness check. The rollback-creates-a-new-version rule is the most common semantic trip — students assume rollback truncates history back to the target version. It does not. Some rotations extend L3 with chef-ranking / order tracking instead of (or in addition to) user permissions — read the prompt carefully before coding. MLE candidates can receive this same Recipe Manager OA before the live Prompting and Engineering with LLMs screen; do not assume the OA rotation is SWE-only. Preparation Run a timed mock of a 4-level OA (any provider) end-to-end in 90 minutes; redo it with a hard cap of 25 min on L1+L2 so L4 has time to land. Pre-write a tiny dataclass-based version store you can reuse: every mutation is versions.append(RecipeVersion(...)), current state is versions[-1]. Drill the rollback case with a synthetic test that rolls back to a version whose old name now belongs to a different recipe — confirm your code returns False without partial state mutation. Memorize the L2 sort key exactly: (len(ingredients), recipe_id_as_sortable). The harness's sort is stable enough that a single composite key is sufficient.