JAVA to C# conversion - PriorityQueue

Question

This question was posted here (https://stackoverflow.com/questions/15881110/java-to-c-sharp-conversion) by a team member but was closed due to the community not having enough information.

Here's my attempt to revive such a question being, How would I go about converting this java extract into C#?

Java Extract:

PriorityQueue<PuzzleNode> openList = new PriorityQueue<PuzzleNode>
           (1,
            new Comparator<PuzzleNode>(){
                public int compare(PuzzleNode a, PuzzleNode b){
                    if (a.getPathCost() > b.getPathCost())
                        return 1;
                    else if (a.getPathCost() < b.getPathCost())
                        return -1;
                    else
                        return 0;
                    }
                }
            );

A sortedList has been thought about but to no avail as I'm unsure how to code it.

I've also tried creating a standard list with a method:

List<PuzzleNode> openList = new List<PuzzleNode>();

//Method to sort the list
public int CompareFCost(PuzzleNode a, PuzzleNode b)
        {
            if (a.getPathCost() > b.getPathCost())
            {
                return 1;
            }
            else if (a.getPathCost() > b.getPathCost())
            {
                return -1;
            }
            else
                return 0;
        }//end CompareFCost

and then calling: openList.Sort(CompareFCost); at appropriate locations, however this doesn't work.

What the code is used for? It orders the objects 'PuzzleNode' depending on a score (pathCost) I have set else where in the program. A while loop then operates and pulls the first object from the list. The list needs to be ordered otherwise an object with a higher pathCost could be chosen and the while loop will run for longer. The objective is to pull the lower pathCost from the list.

I ask for a conversion because it works in Java & the rest of the code has pretty much originated from Java.

Any takers? If you need further info I'm happy to discuss it further.

Perhaps this answer can help: http://stackoverflow.com/questions/102398/priority-queue-in-net I think the only problem there is an alternative to a PriorityQueue, which is quite different from a simple ordered list. — pcalcao, Apr 08 '13 at 14:47
What's the final intent of this? Did you know you can use `LinQ` to do all sorts of `IEnumerable` related operations? Also, what's the difference between the java's `PriorityQueue` and a regular `List`? — Federico Berasategui, Apr 08 '13 at 14:54
@HighCore - Priority queues allow efficient access to and removal of the minimum element. — Lee, Apr 08 '13 at 14:57
Please check edited question which states what it is needed for. I didn't know that, nor do I know how to go about using them at the moment, I'll look into it. — Glitchezz, Apr 08 '13 at 15:00
The minimum element is the element with the lowest/highest priority, in this case. Most priority queues achieve this in O(logN) or O(1) time, while guaranteeing interesting orders of complexity for the rest of the operations (insertion, deletion, etc). — pcalcao, Apr 08 '13 at 15:01
@HighCore - In this case it appears to be the node with the minimum path cost. If the elements in the queue don't have a natural ordering then a custom comparator is required to compare elements. — Lee, Apr 08 '13 at 15:03
Assuming you use a List and are just ordering based on the PathCost, you could use linq: `var orderedList = openList.OrderBy(node => node.getPathCost())` (`.OrderByDescending` if it needs to go the other way). Or, if you want more control over the comparison, look here at the "order by comparer" examples: http://code.msdn.microsoft.com/101-LINQ-Samples-3fb9811b — valverij, Apr 08 '13 at 15:03

spender · Answer 1 · 2013-04-08T15:10:06.730

I suppose you could misappropriate a SortedList something like this:

var openList=new SortedList<PuzzleNode,PuzzleNode>(
    //assumes .Net4.5 for Comparer.Create
    Comparer<PuzzleNode>.Create((a,b)=>{
        if (a.getPathCost() > b.getPathCost())
                    return 1;
                else if (a.getPathCost() < b.getPathCost())
                    return -1;
                else
                    return 0;

    }));
openList.Add(new PuzzleNode());
foreach(var x in openList.Keys)
{
    //ordered enumeration
}
var firstItem = openList.Dequeue();

by creating some extension methods to make things a little more queue-like

static class SortedListExtensions
{
    public static void Add<T>(this SortedList<T,T> list,T item)
    {
        list.Add(item,item);
    }
    public static T Dequeue<T>(this SortedList<T,T> list)
    {
        var item=list.Keys.First();
        list.Remove(item);
        return item;
    }
    //and so on...
}

TBH, I'd probably go for @valverij's answer in the comment to your original question, but if the cost of repeated sorting is prohibitive, this may be what you need.

score 0 · Answer 2 · answered Apr 08 '13 at 15:13

What the code is used for? It orders the objects 'PuzzleNode' depending on a score (pathCost) I have set else where in the program. A while loop then operates and pulls the first object from the list. The list needs to be ordered otherwise an object with a higher pathCost could be chosen and the while loop will run for longer. The objective is to pull the lower pathCost from the list.

1: There's LinQ for that. You don't usually do any of these things in C#, because LinQ does it for you.
- It orders the objects 'PuzzleNode' depending on a score (pathCost)
  
  That's Achieved with LinQ's Enumerable.OrderBy() Extension:
```
//Assuming PathCost is a property of a primitive type (int, double, string, etc)
var orderedlist = list.OrderBy(x => x.PathCost);
```
- The objective is to pull the lower pathCost from the list.
  
  That's achieved using LinQ's Enumerable.Min() or Enumerable.Max() extensions.
```
//Same assumption as above.
var puzzlewithlowestpath = list.Min(x => x.PathCost);
```

here goes my rant about java being incomplete compared to C# because it lacks something like LinQ, but I will not do any more ranting in StackOverflow by now.

Another thing I wanted to mention is that if you are coding in C#, you'd better use C# Naming Conventions, where Properties are ProperCased:

public int PathCost {get;set;}
//or double or whatever

instead of:

public int getPathCost()
public int setPathCost()

JAVA to C# conversion - PriorityQueue

2 Answers2