CODEWITHSUNDEEP
javapriority-queue
vixero
vixero

Reputation: 514

PriorityQueue, insert with priority

I'd like to know how can I add a value to a PriorityQueue with a specific value.

I have a Map<Integer, Integer> // element -> value and I'd like to insert elements to the PriorityQueue with the value priority.

For example:

Map{1=0, 3=5265, 5=22375, 7=4202, 9=233, 11=351, 13=119}

should have this order in the Queue:

{1, 13, 9, 11, 7, 3, 5}

Upvotes: 5

Views: 8047

Answers (1)

John Kugelman
John Kugelman

Reputation: 361625

PriorityQueue expects elements to be comparable to each other. It doesn't explicitly track the priority of each element itself. It just compares them to each other. That means you'll need to the elements and their priorities into the queue in pairs.

One way to do that is to add Map.Entrys directly and create the queue with a custom comparator.

PriorityQueue<Map.Entry<Integer, Integer>> queue =
    new PriorityQueue<>(Comparator.comparing(entry -> entry.getValue()));

queue.addAll(map.entrySet());

Another way would be to create a simple class holding both values that implements Comparable. Something like:

class ElementPriority implements Comparable<ElementPriority> {
    int element;
    int priority;

    @Override public int compareTo(ElementPriority other) {
        return Integer.compare(this.priority, other.priority);
    }
}

Or if you want to get really hacky you could combine each pair of ints into a long holding both values. If you store the priorities in the big end then the elements should naturally sort by priority.

PriorityQueue<Long> queue = new PriorityQueue<>();

map.forEach((element, priority) -> {
    queue.add((priority & 0xFFFFFFFFL) << 32 | (element & 0xFFFFFFFFL));
});

This is highly dubious, but hey, what the heck.

Upvotes: 5

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