Config Merge with Deletions

What you will practice

Requirements

• Keep the public `merge_config(base, override)` function signature intact.
• Return a new dict without mutating `base` or `override`.
• Keep keys that appear in only one input dict.
• Recursively merge values only when both values are dicts.
• When values are not both dicts, the override value wins.
• If an override value is `None`, remove that key from the result.
• Lists must be replaced by override lists, not merged.

Starter files

What the judge checks

• Runs in the python environment with the python-function runner.
• Uses a 2000ms judge budget.
• Behavior rules include: No Mutation, Dicts Merge Recursively, Lists Replace Not Merge, None Deletes Key.

Constraints

• Values may be dicts, lists, strings, numbers, booleans, or None
• Nesting depth is at most 20

Example behavior

base = {"a": 1, "b": {"x": 1, "y": 2}}
override = {"b": {"y": 99, "z": 3}}

{"a": 1, "b": {"x": 1, "y": 99, "z": 3}}

base = {"a": 1, "b": {"x": 1}, "c": 3}
override = {"b": None, "c": {"k": 1}}

{"a": 1, "c": {"k": 1}}

Follow-up

How would you detect and reject cyclic references in input objects?