from collections import deque
# double-ended queue, this may be helpful
# see the docs: https://docs.python.org/3/library/collections.html#collections.deque

classes = {
    'CPSC 230': {'CPSC 231'},
    'CPSC 231': {'CPSC 350', 'CPSC 330'},
    'CPSC 350': {'CPSC 380', 'CPSC 408', 'CPSC 406'},
    'CPSC 330': {'CPSC 351'},
    'CPSC 351': set(),
    'ENGR 101': set(),
    'CPSC 380': set(),
    'CPSC 406': set(),
    'CPSC 408': set()
}

def topological_sort(adjacency_list: dict[str, set[str]]):
    # return the sorted ordering
    return []

print(topological_sort(classes))