Introduce constructor for PriorityQueue with existing collection and custom comparator

[Valeh Hajiyev]

Hi Pavel,

Thanks for the reply. If I understand correctly, I need this change to be
discussed in one of the mailing lists there, so that someone would sponsor
me to create a tracking issue in JBS. Do you know which mailing list is the
most relevant for me to propose the change?

Thanks,
Valeh

On Thu, Dec 14, 2023 at 12:26 AM Pavel Rappo <pavel.rappo at oracle.com> wrote:

> Sorry, there's a necessary process that a PR must follow. You seem to have
> signed OCA already. For the rest, see this resource:
> https://openjdk.org/guide/. In particular, this part:
> https://openjdk.org/guide/#contributing-to-an-openjdk-project.
>
> -Pavel
>
> > On 13 Dec 2023, at 23:09, Valeh Hajiyev <valeh.hajiyev at gmail.com> wrote:
> >
> > Hi all,
> >
> > I have raised the following PR, could someone please help me to get it
> merged?
> >
> > https://github.com/openjdk/jdk/pull/17045
> >
> > More details:
> >
> > This commit addresses the current limitation in the `PriorityQueue`
> implementation, which lacks a constructor to efficiently create a priority
> queue with a custom comparator and an existing collection. In order to
> create such a queue, we currently need to initialize a new queue with
> custom comparator, and after that populate the queue using `addAll()`
> method, which in the background calls `add()` method (which takes `O(logn)`
> time) for each element of the collection (`n` times).  This is resulting in
> an overall time complexity of `O(nlogn)`.
> >
> > ```
> > PriorityQueue<String> pq = new PriorityQueue<>(customComparator);
> > pq.addAll(existingCollection);
> > ```
> >
> > The pull request introduces a new constructor to streamline this process
> and reduce the time complexity to `O(n)`.  If you create the queue above
> using the new constructor, the contents of the collection will be copied
> (which takes `O(n)` time) and then later  `heapify()` operation (Floyd's
> algorithm) will be called once (another `O(n)` time). Overall the operation
> will be reduced from `O(nlogn)` to `O(2n)` -> `O(n)` time.
> >
> > ```
> > PriorityQueue<String> pq = new PriorityQueue<>(existingCollection,
> customComparator);
> > ```
> >
> > Best regards,
> > Valeh Hajiyev
> >
>
>
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