Junio C Hamano <gits...@pobox.com> writes: > I have set of items with two attributes, <X,Y>, and would like to > keep them in some data structure in such a way that it is efficient > to (1) add a new item to the data structure, and (2) pick an item in > a specific order. There can be multiple items that share the same > value for X, or Y, or both X and Y, and it does not matter in what > order items comes out among those that share the same <X,Y>. > > The type of X is totally ordered. The type of Y also usually is, but > Y can take a special value U(nspecified). > > Now on to the "specific" order I want to pick an item. I'd like to > take the item with the largest value of Y in general, and tiebreaking > on the value of X which also I prefer to take from larger to smaller. > > But with a twist. > > When I am picking an item <X=n,Y=m>, there should be no item > remaining in the data store with a value of Y that is smaller than m > (duplicates are allowed, so there can still be items with Y=m), and > also when I am picking <X=n,Y=m>, there should be no item with > Y=Unspecified that has a value of X that is equal or smaller than n. > > E.g. if I have these 6 items (ignore the lines between the items for > now): > > <104,U>--<105,U>--<106,4> > / > <101,U>--<100,U>--<102,3>--<104,4> > > I would want to pick them up in this order: > > <106,4> <105,U> <104,U> <104,4> <102,3> <101,U> <100,U>

## Advertising

Note that with the above specification, a possible solution is to show all the items with Y=Unspecified before showing others, but that would not be ideal for the intended use case; pretending Y=U as if Y=max_range is not a usable workaround. This is "I create a stream of items with specified Y in descending order. There are some items with Y=Unspecified and I want to find appropriate places to mix the latter into that stream". Because the desired ordering is not a total order, I need to go to the "pair of priority list" route, I think. > > I see how this can easily be done by using a two priority lists, > i.e. one for items with Y=Unspecified that is sorted by X, and the > other for all other items that is sorted by <Y,X>. Peek the top of > both, and pick the top of the former until its X is smaller than the > value of X of the top of the latter, otherwise pick the top of the > latter. I am wondering if I can use less complex data structure, > like a single ordered sorted array, with a clever comparison > function. > > For the curious, the items in the above picture represents commits, > and lines are ancestry chains between them. I am thinking how we can > extend the still_interesting() function with an optional generation > number. -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html