So I want to use the smallest key as the priority and then return the VALUE of that corresponding key:
import javafx.util.Pair;
import java.util.PriorityQueue;
public class Test
{
public static void main (String[] args)
{
int n = 5;
PriorityQueue <Pair <Integer,Integer> > l = new PriorityQueue <Pair <Integer,Integer> > (n);
l.add(new Pair <> (1, 90));
l.add(new Pair <> (7, 54));
l.add(new Pair <> (2, 99));
l.add(new Pair <> (4, 88));
l.add(new Pair <> (9, 89));
System.out.println(l.poll().getValue());
}
}
The output Im looking for is 90 because 1 is the smallest key. Its fine even if the value is used as the priority and the key is returned because I can just swap the data if neccessary. I want to display key/value using value/key as a priority (minimum value in this case). I do not know how this can be done in this scenario. This works fine in C++.
You need to use Comparator
which will be used to order this priority queue.
Use Comparator.comparing()
and pass Method reference
of comparing parameter when create the PriorityQueue
PriorityQueue<Pair<Integer,Integer> > pq=
new PriorityQueue<Pair<Integer,Integer>>(n, Comparator.comparing(Pair::getKey));
Or
You can use lambda expression
PriorityQueue<Pair<Integer,Integer> > pq=
new PriorityQueue<Pair<Integer,Integer>>(n,(a,b) -> a.getKey() - b.getKey());
Alternative, use custom Pair
class that implements Comparable
.
class Pair implements Comparable<Pair> {
Integer value;
Integer index;
public Pair(Integer value, Integer index) {
this.value = value;
this.index = index;
}
@Override
public int compareTo(Pair o) {
return value - o.value;
}
}
and then usage
// Add elements
queue.add(new Pair(valueKey, index));
// do it for all your elements
final Pair min = queue.poll();
Integer index = min.index;
Integer value = min.value;
// Do with them what you want.
I used PriorityQueue in leetcode challenge. https://leetcode.com/problems/merge-k-sorted-lists/discuss/630580/Using-PriorityQueue-in-Java
And this is full example https://github.com/yan-khonski-it/leetcode/blob/master/src/main/java/com/yk/training/leetcode/merge_sorted_lists/PriorityQueueSolution.java
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