Question

Say there’s a list. Each item in the list has a unique id.

List [5, 2, 4, 3, 1]

When I remove an item from this list, the unique id from the item goes with it.

List [5, 2, 3, 1]

Now say I want to add another item to the list, and give it the least lowest unique id.

What’s the easiest way to get the lowest unique id when adding a new item to the list?

Here’s the restriction though: I’d prefer it if I didn’t reassign the unique id of another item when deleting an item.

I realise it would be easy to find the unique id if I reassigned unique id 5 to unique id 4 when I deleted 4. Then I could get the length of the list (5) and creating the new item with the unique id with that number.

So is there another way, that doesn’t involve iterating through the entire list?

EDIT:

Language is java, but I suppose I’m looking for a generic algorithm.

Answer 1

An easy fast way is to just put your deleted ids in a priority queue, and just pick the next id from there when you insert new ones (or use size() + 1 of the first list as id when the queue is empty). This would however require another list.