Polynomial time complexity

polynomial.py

from typing import Any, List, Set


def find_duplicates(list_: List[Any]) -> Set[Any]:
    """Find all duplicate items in a list."""
    
    # Initialize a set to hold the duplicate items
    duplicates = set()

    # Check each item in the list against every other item in the list
    for index_1, item_1 in enumerate(list_):
        for index_2, item_2 in enumerate(list_):
            if index_1 != index_2 and item_1 == item_2:
                duplicates.add(item_1)

    # Return the set of duplicate items
    return duplicates