Flatten and unflatten nested Python structures

You are given nested Python data structures used to represent hierarchical data.

Supported node types

• Parent/container nodes can be:
  • list
  • tuple
  • dict
• Leaf nodes are always integers ( int ).

For deterministic behavior, traverse containers in this order:

• list / tuple : left-to-right
• dict : iterate keys in the dictionary’s iteration order (assume it is deterministic for the input)

Part A — Flatten

Task: Write a function flatten(structure) -> list[int] that extracts all integer leaves in traversal order into a single flat list.

Example Input:

{'a': [1, 2, 3], 'b': {'c': [{'d': 4}], 'e': 5}}

Output:

[1, 2, 3, 4, 5]

Part B — Unflatten

This is the inverse operation.

Inputs:

• flat_list : a list of integers (new values)
• template : a nested structure (same allowed types as above) whose shape should be reproduced

Task: Write a function unflatten(flat_list, template) that returns a new object with the exact same nested shape and container types as template, but with each integer leaf replaced by values from flat_list in traversal order.

Assumptions / constraints:

• flat_list contains exactly the number of integers required by template (or define and implement behavior if it has too few/too many).

Example (conceptual) Given:

• flat_list = [6, 7, 8, 9, 0]
• template is a nested dict/list/tuple structure with 5 integer leaves (e.g., corresponding to leaves at keys/positions a, b, c, d, e in traversal order)

Output:

• a new structure with the same shape as template , whose leaf values become 6, 7, 8, 9, 0 in that order.