Questions tagged [priority-queues]
The priority-queues tag has no usage guidance.
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If both could be implemented with the other, what are the differences between priority queues and binary heaps?
I've red that a binary heap can be implemented using a priority queue. I've also red the opposite, that a priority queue can be implemented using a binary heap.
This seems strange to me as ...
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1answer
36 views
What is the anayslsis that a heap's optimal branching factor is 2 <= factor <=5?
I'm reading the book Advanced Algorithms and Data Structures and it makes the claim that the optimal branching factor for a heap is 2 <= D <= 5 and that it is ...
2
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2answers
56 views
Given n positive integers, pick two elements and subtract each by one with one operation. Find max operations
Problem Description: we have an array of n positive integers and in one operation we have to choose two elements in the array and decrease them by 1. (Elements on which we are performing this ...
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1answer
30 views
Build a priority queue using dictionary
QUESTION: Can we Implementing priority queue with hash table please?
As I understand, dictionary/hash table does not have sorting mechanism inside. It adds pairs of $<key,value>$ to hash table. ...
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21 views
Accessing Array-based vs LinkedList PriorityQueue
Question 1: Suppose we have the two priority queues, or we have two implementations available. One implementation uses an array to maintain the entries in the priority queue, while the other uses a ...
2
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1answer
37 views
Dijkstra's Algorithm Same Node Added Multiple Times to Priority Queue
In the this discussion of Dijkstra's Algorithm appear the following comments:
...
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1answer
58 views
Minimum time to finish all meetings
what algorithm would you use to solve this problem which I recently faced in an interview?
There's a council where people go to have meetings. A person comes at time x and needs to be in a meeting for ...
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0answers
21 views
How to find diffrenet ways to implement merge and delete_min operation in binomial heap?
I have searched on the internet to find different ways to learn binomial heap operations. What I have found is not quite helpful for me.For example, for delete min operation the algorithm says:
...
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2answers
75 views
Max-Heap PriorityQueue to keep the k highest items and return them in descending order
I have created a custom implementation for PriorityQueue using max-heap and everything works fine.
But now i want to change it and keep only the k highest objects in the heap after every insertion. I ...
1
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1answer
116 views
Is there an algorithm for random sampling from a priority queue with probability proportional to priority?
Suppose I want to randomly sample from a large set of items, each of which has a "score". I want my probability of sampling to be proportional to the score. One simple way to achieve this ...
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30 views
data structure Q with priotry queue which allow us to find the median in $O(1)$ and the data structure need to support the following operations
I've got this question from an exercise and i'm not sure if it is possible to do so
Think of new data structure Q with priotry queue which allow us to find the median in $O(1)$ and the data structure ...
3
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1answer
267 views
What are the disadvantages of Fibonacci Heaps?
A Fibonacci heap is a data structure for priority queue / heap operations. It seems to have the best complexity for all operations:
Since it has the best performance, why not use it everywhere?
What ...
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1answer
35 views
Constructing a data structure supporting prioritized key lookup
so this is more or less a shot in the dark as I am feeling stuck. Maybe some of you have an idea which helps.
Here is the problem description (pseudo formal):
I want to have a structure $T = \{ \hat{...
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368 views
Monotone priority queues
I'm a little confused about how monotone priority queues work.
As far as I understand:
A queue is a FIFO data structure
A priority queue is a queue where the current element of highest (or lowest) ...
3
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2answers
446 views
Implementing an efficent priority queue using only stacks
Is it possible to implement an efficient priority queue (as efficient as a heap) only using the stack data structure?
The usual efficiency for a priority queue which is implemented using a heap is :
...
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1answer
236 views
Priority Queue Using Stack
Can one build a priority queue using stacks, such that the priority queue has the same complexity for each operation.
Could it be done? If so how? If not what is the best solution that can be done?
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2
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1answer
83 views
Numerical Accuracy & Sorting Algorithms?
Sedgewick and Wayne talk about how sorting algorithms and, specifically, priority queues are used in devising ways to improve accuracy in floating-point calculations: https://algs4.cs.princeton.edu/...
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22 views
How to compute the general term formula for the number of full binary tree heaps that can be formed with distinct elements?
The number of possible heaps that are full binary trees of height $h$ and can be formed with ($n = 2^h - 1$) distinct elements can be computed by recursion:
$$ a_h = {2^h - 2 \choose 2^{h - 1} - 1} a_{...
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1answer
948 views
Dijkstra without decrease key
I was reading through this paper, "Priority Queues and Dijkstra's Algorithm" by Mo Chen et al., which suggests using Dijkstra's without edge relaxation, but to rather to just insert new ...
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0answers
485 views
Making an array increasing by modifying elements
I am trying to solve a problem on codeforces. Given an integer array $a_1,\ldots,a_n$, our goal is to find the minimal number of instructions, each of which increments or decrements a single entry, ...
2
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2answers
151 views
Why can't we replace Dijkstra's priority queue with a regular queue?
I am confused why we can't simply use a normal queue instead of a priority queue for Dijkstra's. I agree that you can find the shortest path in fewer iterations of the while loop using a priority ...
3
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1answer
33 views
Parallelization of priority queue-based algorithms
There's a number of algorithms that operate by maintaining and consuming a priority queue of "events". I'm thinking primarily of geometric algorithms, particularly sweep-line algorithms like Bentley-...
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87 views
When inserting an element in a priority queue and the heap size is already at max capacity, should you output an error OR increase the array size?
I'm currently learning about how to implement priority queues using heaps, but I've hit a wall while trying to implement the insertion operation. Assume that the size of the array storing the ...
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1answer
99 views
Priority queue with a buffer for delayed insertion and other tweaks
I was thinking of ways to optimise a (heap-based) priority queue in certain scenarios, like in best-first path search algorithms (Dijkstra, A*, etc.).
One possible optimisation is to delay insertions ...
0
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1answer
75 views
Short Fibonacci Heap
Is it possible to create a Fibonacci Heap that has exactly 5 nodes: one root node and 4 children of that root?. If yes please explain the sequence of operations to do so. If it is not possible then ...
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1answer
82 views
An algorithm to drop low-priority items from a heap-based priority queue
I am looking for an efficient algorithm to drop from a complete binary min heap all items whose weight exceeds a given value. (Or, equivalently, to drop from a priority queue realised by such a heap ...
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727 views
Merging balls interview problem
Here is an interview problem about balls rolling towards buckets from Sprinklr Interview Experience at GeekforGeeks.
You are given $n$ balls on the table and all the balls are rolling towards the ...
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1answer
67 views
Heap operating in time $\Gamma^{-1}(n)^2$
I have a priority queue implementation which I claim has the following worst case asymptotic run-times for the given operations:
PEEK_MIN …………………………… O(1)
POP_MIN…………………………… O( (INVERSE_Γ(n)) ^2).
...
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2answers
489 views
Is there a name for this priority queue data structure?
While watching a sports tournament, I noticed that the tournament tree looks a lot like a heap. I came up with the following data structure: A complete binary tree where the leaves are elements of ...
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1answer
1k views
Why is a heap better than a linked list for implementation of a priority queue?
Using a heap, you have O(log(n)) insertion and O(log(n)) removal. Using a linked list, you have O(n) insertion and O(1) removal.
Why is it better to have log-n for both than n for one and constant ...
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0answers
75 views
How priority queue is used in Dijsktra algorithm?
I have difficulties understanding how the priority queue is used in Dijkstra algorithm. Wikipedia lists 3 operations performed on priority queue:
add_with_priority(),
extract_min(),
...
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2answers
163 views
Sorting in a Priority Queue
Does a priority queue Queue<K,V> always sort its elements based on the value of each element or its key?
I know than the priority in the queue is based on ...
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1answer
54 views
Complexity of closest set of points in plane problem
Given a set of points on a plane find the set of $n$ points that are closest to the origin. (Points are pairs of integers.)
Input: list of points.
Initialize a priority queue $Q$, where ...
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2answers
142 views
Priority queue of constant size fit for extraction of K highest priority elements
In an algorithm I'm designing, I need to do this cycle on a priority queue of constant size N many times, as quickly as possible:
get $K$ highest priority elements (do on them some outside ...
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0answers
464 views
How would a priority queue be implemented in a functional programming language?
How would a priority queue be coded efficiently in a functional programming language? I'm new to functional programming, but I'm having difficulty understanding how a data structure that seems to ...
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2answers
812 views
Correct term for a priority queue with unique elements
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 ...
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1answer
175 views
Leftist Tree initialization in O(n) time
In the book Handbook of Data Structures and Applications, section 5.2.5, (copy of the relevant section available here) about leftist queues, the author(s) state the following:
For the complexity ...
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Find K largest elements using a priority queue [duplicate]
Say we have a Priority Queue of size 1000 that is implemented using Max Heap.
Now if i want to get the top 5 elements, the most laid back method is to poll the maximum 5 times, resulting in a set of ...
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1answer
396 views
Bucket Priority Queues with large integers for $O(1)$ insert and extract~min?
I recently got into a discussion about Priority Queues when the requirements allow for "best effort" removal (i.e. the removed key may not always be THE very highest priority, but it is relatively ...
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78 views
Why do we need increase_key procedure in max priority queue?
Since if I want to increase the priority of a specific node, how do I find the node without linear searching it.
I need to pass the index to this function, which is in a way a bottleneck. So the ...
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185 views
Devise algorithm to travel destinations in a way that you always have enough money for the next destination (getting paid at each destination as well)
This problem probably falls under some category of algorithms but I don't know which.
A given restaurant has $b_1..b_n$ branches around the world. A food critic has to travel all of the branches.
...
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3k views
Bubble down implementation for min-heap
While going through bubble_down implementation for min-heap in The Algorithm Design Manual By Steven Skiena, since routine ...
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2answers
806 views
How to classify simple priority queue algorithm
I have a simple priority queue algorithm that I implemented, and I doubt it's new
but I haven't been able to classify it. Wondering if I could get some help with classifying it! Once I classify it I ...
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0answers
403 views
Unique integer priority queue with both $O(1)$ insert and extract-min?
I'm aware of the two questions prioritizing inserts and extracts individually, each in $O(1)$ time, but does there exist a unique integer priority queue algorithm for the range $[0, n)$ that can do ...
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1answer
562 views
Best data structure for a queue with random reads?
Well, it's not exactly a queue if it allows for random reads. This question is about a data structure which behaves like a queue for insertions and a sorted dictionary for reads.
Imagine an algorithm ...
2
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1answer
57 views
Efficient haircuts
I have a real vector $v$. From this vector, I want to extract a sequence of integers, $ix$. The first integer is found by, $ix_0=argmax(v)$. 1 is then subtracted from $v_{ix_0}$, and the process is ...
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9k views
Finding the median in a heap
Given a binary heap $H$, indexed in $[1..n]$, whose elements are integers, is there a way to quickly find its median in $O(\log n)$-time?
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Why in a min priority queue (heap based) it is called "decrease-key" and not just "set-key"?
When you call decrease-key in a min priority queue, you are basically setting the key, you can accidentally put a higher key, right? so why isn't it called "set-key" or "update-key"? why (according to ...
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1answer
869 views
Heap-like data structure allowing peek at largest & smallest
For the purpose of implementing an optimization algorithm (finding the minimum of a multivariate function) I want to create a data structure that supports the following operations:
load from array
...
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2answers
8k views
How to calculate probability of packet loss and drop rate?
In a queuing system (M/M/1) with a finite packet capacity $z$, how do you determine the probability of packet loss if we assume that packets are dropped when the system is full? Packets arrive with a ...
