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
> I would want to pick them up in this order:
> <106,4> <105,U> <104,U> <104,4> <102,3> <101,U> <100,U>
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
> 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
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