Javascript priority queue with decrease key operation

Javascript priority queue with decrease key operation

By : user2954977
Date : November 22 2020, 10:33 AM
this one helps. I found out the following resource for exactly what I have been looking for:
code :

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SQL priority queue operation - any pitfalls?

SQL priority queue operation - any pitfalls?

By : Rd Hilman Hermarian
Date : March 29 2020, 07:55 AM
I hope this helps . The SELECT / UPDATE combination listed seems to address the concrrency issue with the UPDATE's WHERE clause. I would however lean toward a stored procedure if that were acceptable: depending on the sql flavour, the stored proc could get rid of the concurrency problem with an atomic "UPDATE ... RETURNING id INTO... ".
Regarding the states, if they are something like:
Priority queue, overloading less operation

Priority queue, overloading less operation

By : Hector Romero Brand
Date : March 29 2020, 07:55 AM
may help you . Check out this reference. By default, the top element is the largest element. If you want opposite behavior, you must use different comparison function, just as you've done.
How to implement O(logn) decrease-key operation for min-heap based Priority Queue?

How to implement O(logn) decrease-key operation for min-heap based Priority Queue?

By : z.ali
Date : March 29 2020, 07:55 AM
With these it helps You can do following: store a hashmap inside your heap that maps your heap values to heap indexes. Then you should extend your usual heap-logic just a bit:
code :
on Swap(i, j): 
    map[value[i]] = j; 
    map[value[j]] = i;
on Insert(key, value): 
    map.Add(value, heapSize) in the beginning;
on ExtractMin: 
    map.Remove(extractedValue) in the end;
on UpdateKey(value, newKey): 
    index = map[value]; 
    keys[index] = newKey; 
Can this code be modified to make the priority queue decrease its key in O(logn) time?

Can this code be modified to make the priority queue decrease its key in O(logn) time?

By : Mark Shavlik
Date : March 29 2020, 07:55 AM
will be helpful for those in need As @DavidEisenstat indicates in comments, you don't need decrease_key if you just add multiple records to the heap.
You also need to keep track of which nodes you've popped off the priority queue, so you can only process a node the first time you see it. (Otherwise the worst case complexity increases)
code :
def dijkstra(G, src, dist, V):

    for v in range(V):
        dist[v] = float('inf')
    dist[src] = 0

    pq = [(0,src)]
    seen = [False]*V

    while pq:
        u = heapq.heappop(pq)[1]
        if seen[u]:
        seen[u] = True
        for v, w in G[u]:
            if dist[u] + w < dist[v]:
                dist[v] = dist[u] + w
                heapq.heappush( pq, (dist[v],v) )
Why doesn't max-priority queue have DECREASE-KEY?

Why doesn't max-priority queue have DECREASE-KEY?

By : Arun Salian
Date : March 29 2020, 07:55 AM
hop of those help? Nothing is stopping you to implement DECREASE-KEY in your binary heap. It can be done in O(log N) without breaking any invariants.
My guess is that it isn't included, because it's not needed very often.
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