Flatten a Nested Dictionary

mediumpy_datastructures

Implement three flatteners of an arbitrarily nested dict whose leaves are ints: turn it into (dotted_key, value) pairs, e.g. {"a": {"b": 1}} → [("a.b", 1)]. Key order in the result doesn't matter.

traverse_dictionary_immutable(dct, prefix="") — recursion that returns a new list.
traverse_dictionary_mutable(dct, result, prefix="") — recursion that appends to the given result list (returns None).
traverse_dictionary_iterative(dct) — no recursion: use an explicit stack so it survives very deep nesting (100000 levels).

Don't modify the input dict.

Your solution

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Hints

Hint 1

At each level join the path with '.'; recurse into dict values, otherwise emit (full_key, value).

Hint 2

For the iterative version keep an explicit stack of (prefix, subdict) so deep nesting can't overflow the recursion limit.