spirited_away_'s blog

How to delete elements in a priority queue ?

By spirited_away_, history, 5 years ago, In English

I want to delete some element in a priority queue not at the top, how should i do? can someone suggest any method, in constant or logarithmic time. How to handle duplicates while removing

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5 years ago, # |
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It's not possible. In a heap(or pq) finding an element in itself is linear.

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    5 years ago, # ^ |
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    OK! can we implement it on our own such that it work in logarithmic time, is it possible?

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      5 years ago, # ^ |
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      Use multiset

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        5 years ago, # ^ |
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        but suppose we use multiset which consists of s = {3 , 2 , 2 }, now if we want to delete just one 2 from it, its not possible because i think both 2's will be deleted.

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      5 years ago, # ^ |
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      Use set or multiset . Now to get the element on top you can call set_name.rbegin() . To delete some elements just delete it if you know that they are in set . Learn about how to delete an element in mulitset because if you delete an element in multiset by value it will delete all the elements with that value .

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3 years ago, # |
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Is it possible to delete any random elements from multiset ,suppose multiset contains 10 elements , so is it possible to delete, say 5th element?

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3 years ago, # |
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use multiset instead

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21 month(s) ago, # |
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You can remove the top easily.

If you want to delete another element, you can do it "lazily": when you are given an element to delete from the priority_queue, store somewhere else that this element no longer belongs there (for examplein a map or in a vector of booleans). Then, when you have a "top" request on the priority queue, pop until you reach an element actually still in the queue, according to the other data structure.

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