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scalapriority-queue

Create a PriorityQueue that contains triples, and returns the minimum third element in Scala?

I have a Priority Queue in Scala that I define below. My goal is that when I call dequeue I get the triple that has the most minimum third element in that triple. I figured that using Ordering is the way to go, but I cannot seem to get it to work. 

import scala.collection.mutable.PriorityQueue

def orderByWeight(lst : (Int, Int, Int)) = lst._3

val pq = new PriorityQueue[(Int, Int, Int)]()(Ordering.by(orderByWeight))

var x = ListBuffer((0,1,2), (0,2,3), (0,3,4))

x.map(i => pq.enqueue(i))

I am confused on what my orderByWeight function should be. For the code above, the desired output if I call pq.dequeue should be (0, 1, 2). Note x is ordered at random. Any ideas?

Solution

  • If you want all the 3-tuples dequeued in order of smalled 3rd element to largest, I think this is all you need.

    val pq = PriorityQueue[(Int, Int, Int)]()(Ordering.by(-_._3))

    If you need an ordered output in case of 3rd-element ties, you can expand it.

    var x = ListBuffer((0,1,2), (0,2,3), (0,3,4), (1,0,2))
val pq = PriorityQueue(x:_*)(Ordering[(Int, Int)].on(x => (-x._3, -x._2)))