Besides requiring the inheritance, it also forbid doublons in your data structure.

This doesn't seem complicated at all. You have a doubly-linked list and a hash_map that given a location provides an iterator to the element in the list. O(1) to find an element and O(1) to remove it. Adding an element is ammortized O(1) (some rehashing might happen).

Quote: Original post by Steadtler
Besides requiring the inheritance, it also forbid doublons in your data structure.

yes, but as I said, this is for special case, and such things are stated in the specs. (tho this was private stuff and no body else will ever use it)