Unflatten: Refill a Nested Template Structure with Values from a Flat List

Problem: Unflatten a Nested Template Structure Given a flat list of integers and a nested template structure, refill the template’s leaf integer positions in order to produce a new object with the same “shape”. Input flat_list: a list of integers of length N. structure: a nested template object composed of list / tuple / dict. Constraint: all leaf nodes in the template are integers (their values are placeholders only). Output Return a new object new_structure such that: Container types match the template at every position (list stays list, tuple stays tuple, dict stays dict). Each leaf integer is replaced by the next value from flat_list in traversal order. Traversal / Ordering Rules For list / tuple: left-to-right element order. For dict: follow the dictionary’s key iteration order (Python dict iteration order). Error Handling If flat_list has fewer values than required by the template: raise an error. If flat_list has more values than required: raise an error. Example Given: flat_list = [6, 7, 8, 9, 0] structure = {'a': [1, 2, 3], 'b': {'c': [{'d': 4}], 'e': 5}} Output: {'a': [6, 7, 8], 'b': {'c': [{'d': 9}], 'e': 0}} Constraints Number of leaf integers N: 1 ≤ N ≤ 2 * 10^5 Nesting depth D: 1 ≤ D ≤ 10^4 Requirements O(N) time. Preserve the template structure; do not mutate the input template unless explicitly stated. Example Input [6,7,8,9,0] {'a': [1, 2, 3], 'b': {'c': [{'d': 4}], 'e': 5}} Output {'a': [6, 7, 8], 'b': {'c': [{'d': 9}], 'e': 0}}