Changing Java PriorityQueue to a Max PQ [duplicate]

Answer 1

Use Java's Collections.reverseOrder() comparator.

Java Reference

Answer 2

If you have an existing comparator you could create a generic inversing comparator.

public class InverseComparator<T> implements Comparator<T> {
    private final Comparator<T> delegate;

    public InverseComparator(Comparator<T> delegate) {
        this.delegate = delegate;
    }

    public int compare(T x, T y) {
        return delegate(y, x);
    }
}

Answer 3

Not sure what you mean by elegant but when I want a PQ implemented like a MaxHeap (used in Dijkstra's) I just use an inline comparator constructor.

PriorityQueue<Integer> PQ= new PriorityQueue<Integer>(20, new Comparator<Integer>(){
            public int compare(Integer o1, Integer o2){
                return o2 - o1;
            }
        });

It's simple enough for anytime I'm looking for something simple and only want to use the Comparator once.

Answer 4

Here is a code snippet using Collections.reverseOrder()-

    PriorityQueue<Integer> maxPQ = new PriorityQueue<Integer>(20,Collections.reverseOrder());

You also need to provide the initial capacity of the Priority Queue (20 here) along with the Comparator.