def find_duplicate_inds(list_with_duplicates: list):
    """Find indices of duplicates in a list.

    :param list_with_duplicates: list containing duplicate items
    :type list_with_duplicates: list
    :return: list of duplicate indices, list of unique items (parents of duplicates)
    :rtype: list and list
    """
    found = []
    foundind = []
    badind = []
    parentind = []
    for i, item in enumerate(list_with_duplicates):
        try:
            parentind.append(foundind[found.index(item)])
            badind.append(i)
        except ValueError:
            found.append(item)
            foundind.append(i)
    return badind, parentind
