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[Learn more about Teams](https://stackoverflow.co/teams/) # [Correct term for a priority queue with unique elements](https://cs.stackexchange.com/questions/91442/correct-term-for-a-priority-queue-with-unique-elements) [Ask Question](https://cs.stackexchange.com/questions/ask) Asked 7 years, 4 months ago Modified [2 years ago](https://cs.stackexchange.com/questions/91442/correct-term-for-a-priority-queue-with-unique-elements?lastactivity "2023-08-25 18:15:09Z") Viewed 2k times 1 \$\\begingroup\$ Is there a standard term for a priority queue which can only hold a single occurrence of any element? This would be a priority queue for which operations such as "raise the priority of element `x` to the new value `p`" would make sense. In this kind of an abstract container, if you insert some element ("key", but not in the sense of "priority key") with some priority, you cannot insert it again until it is extracted, but you can update its priority. I would also like to know if there is some established interface for this kind of a priority queues. - [data-structures](https://cs.stackexchange.com/questions/tagged/data-structures "show questions tagged 'data-structures'") - [terminology](https://cs.stackexchange.com/questions/tagged/terminology "show questions tagged 'terminology'") - [priority-queues](https://cs.stackexchange.com/questions/tagged/priority-queues "show questions tagged 'priority-queues'") [Share](https://cs.stackexchange.com/q/91442 "Short permalink to this question") Cite [Improve this question](https://cs.stackexchange.com/posts/91442/edit) Follow [edited May 3, 2018 at 9:29](https://cs.stackexchange.com/posts/91442/revisions "show all edits to this post") Alexey[Alexey](https://cs.stackexchange.com/users/27348/alexey) asked May 2, 2018 at 20:24 [](https://cs.stackexchange.com/users/27348/alexey) [Alexey](https://cs.stackexchange.com/users/27348/alexey)Alexey 25111 silver badge1313 bronze badges \$\\endgroup\$ 5 - 1 \$\\begingroup\$ Not that I know of. That operation makes sense even without that condition (you just need a way to identify the element you are talking about, which could be done e.g. with a pointer or in some other way). \$\\endgroup\$ D.W. – [D.W.](https://cs.stackexchange.com/users/755/d-w "168,434 reputation") ♦ 2018-05-02 20:37:56 +00:00 Commented May 2, 2018 at 20:37 - \$\\begingroup\$ IMO it makes little sense to use a PQ to store and move around elements rather than pointers in such case. If i can identify elements in the PQ, it means that they are unique somehow. \$\\endgroup\$ Alexey – [Alexey](https://cs.stackexchange.com/users/27348/alexey "251 reputation") 2018-05-02 20:51:15 +00:00 Commented May 2, 2018 at 20:51 - 1 \$\\begingroup\$ [ceur-ws.org/Vol-1525/paper-13.pdf](http://ceur-ws.org/Vol-1525/paper-13.pdf) \$\\endgroup\$ HEKTO – [HEKTO](https://cs.stackexchange.com/users/11850/hekto "3,183 reputation") 2018-05-02 21:37:20 +00:00 Commented May 2, 2018 at 21:37 - \$\\begingroup\$ "single occurrence of any element" - based on what? Do you assume that all the elements have a *key*, which must be unique all over the queue? Can you please clarify? \$\\endgroup\$ HEKTO – [HEKTO](https://cs.stackexchange.com/users/11850/hekto "3,183 reputation") 2018-05-02 21:47:07 +00:00 Commented May 2, 2018 at 21:47 - \$\\begingroup\$ @D.W., i've realised that it can indeed be more efficient to keep the data associated to the key in this "keyed" priority queue, rather than in a separate key-value store (less search-by-key operations to perform). Maybe i will go with "priority queue with unique keys" or "indexed priority queue"... \$\\endgroup\$ Alexey – [Alexey](https://cs.stackexchange.com/users/27348/alexey "251 reputation") 2018-05-03 18:26:40 +00:00 Commented May 3, 2018 at 18:26 [Add a comment](https://cs.stackexchange.com/questions/91442/correct-term-for-a-priority-queue-with-unique-elements "Use comments to ask for more information or suggest improvements. Avoid answering questions in comments.") \| ## 3 Answers 3 Sorted by: [Reset to default](https://cs.stackexchange.com/questions/91442/correct-term-for-a-priority-queue-with-unique-elements?answertab=scoredesc#tab-top) 3 \$\\begingroup\$ I don't know of a name for the abstract data structure. There is a well-established implementation of what you describe, though: *treaps*, a combination of BST and heap (i.e. priority queue). This is with priority and value/key being different things, though. If priority and value are the same, use any priority queue and add uniqueness, i.e. by combining it with a set/dictionary data structure. (Treaps degenerate to sorted lists in this case.) [Share](https://cs.stackexchange.com/a/91457 "Short permalink to this answer") Cite [Improve this answer](https://cs.stackexchange.com/posts/91457/edit) Follow answered May 3, 2018 at 8:53 [](https://cs.stackexchange.com/users/98/raphael) [Raphael](https://cs.stackexchange.com/users/98/raphael)Raphael 73\.3k3131 gold badges183183 silver badges403403 bronze badges \$\\endgroup\$ 0 [Add a comment](https://cs.stackexchange.com/questions/91442/correct-term-for-a-priority-queue-with-unique-elements "Use comments to ask for more information or suggest improvements. Avoid comments like “+1” or “thanks”.") \| 1 \$\\begingroup\$ Does `PriorityQueueSet` sounds good? A sample signature of Java implementation /\*\* - A priority queue that also maintains a set of unique entries. - @param type of the key to identify the entry - @param type of the entry - keyExtractor is used to extract the key from the entry - valueComparator is used to sort the entries in the queue \*/ public class PriorityQueueSet\<K, V\> extends PriorityQueue [Share](https://cs.stackexchange.com/a/161768 "Short permalink to this answer") Cite [Improve this answer](https://cs.stackexchange.com/posts/161768/edit) Follow answered Aug 25, 2023 at 18:15 [](https://cs.stackexchange.com/users/162646/sandeep-thar) [Sandeep Thar](https://cs.stackexchange.com/users/162646/sandeep-thar)Sandeep Thar 11122 bronze badges \$\\endgroup\$ 1 - \$\\begingroup\$ Interesting idea. Maybe just `PrioritySet` then... \$\\endgroup\$ Alexey – [Alexey](https://cs.stackexchange.com/users/27348/alexey "251 reputation") 2023-08-25 18:18:16 +00:00 Commented Aug 25, 2023 at 18:18 [Add a comment](https://cs.stackexchange.com/questions/91442/correct-term-for-a-priority-queue-with-unique-elements "Use comments to ask for more information or suggest improvements. Avoid comments like “+1” or “thanks”.") \| 0 \$\\begingroup\$ Let me clarify first that by "unique elements" I meant elements unique by their identities, not by their "values." (In case of mutable objects, distinct mutable objects may at some moment have identical "values.") The identities of elements have to be maintained while the elements are being moving inside the priority queue implementation. I've decided to go with *indexed priority queue*. It turns out that a similar term is used in [*Algorithms*](https://algs4.cs.princeton.edu/home/) textbook by Robert Sedgewick and Kevin Wayne: they call it [*index priority queue*](https://algs4.cs.princeton.edu/24pq/). I've also checked out [*Algorithm Design*](https://archive.org/details/AlgorithmDesign1stEditionByJonKleinbergAndEvaTardos2005PDF/page/n90) by Jon Kleinberg et Éva Tardos and [*Introduction to Algorithms*](https://mitpress.mit.edu/books/introduction-algorithms-third-edition) by Cormen et al, but they do not use any special term for this kind of a PQ, and just keep calling it a priority queue. [Share](https://cs.stackexchange.com/a/105831 "Short permalink to this answer") Cite [Improve this answer](https://cs.stackexchange.com/posts/105831/edit) Follow [edited Mar 20, 2019 at 16:16](https://cs.stackexchange.com/posts/105831/revisions "show all edits to this post") answered Mar 20, 2019 at 13:43 [](https://cs.stackexchange.com/users/27348/alexey) [Alexey](https://cs.stackexchange.com/users/27348/alexey)Alexey 25111 silver badge1313 bronze badges \$\\endgroup\$ [Add a comment](https://cs.stackexchange.com/questions/91442/correct-term-for-a-priority-queue-with-unique-elements "Use comments to ask for more information or suggest improvements. Avoid comments like “+1” or “thanks”.") \| Start asking to get answers Find the answer to your question by asking. 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