Introduce constructor for PriorityQueue with existing collection and custom comparator

[Pavel Rappo]

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-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
>