java- sort linked list of strings based on their assigned integer values

Question

I have a linked list of strings, each of those strings has an integer value from calculation. To explain things easier, I have a linked list of strings representing nodes. Each node has a distance. To get the distance, you use a method I created in my program to return that node's distance. I want that linked list to be sorted by each of the string's distance, from lowest to highest. How would I do that? Here is a psedocode

Queue<String> someStringList = new LinkedList<String>();

...

for each of the nodes in the list

String node = ((LinkedList<String>) someStringList).get(i);
distance = theNodesDistance(node);
sort the linked list by the node's distance
...

public int theNodesDistance(String str){
return distance;

}

Answer 1

The first option is to create a comparator and then sort the collection. I would do something like:

  public static void main(String... arg) {
        LinkedList<String> someStringList = new LinkedList<>();

        someStringList.add("2");
        someStringList.add("1");

        System.out.println(someStringList);

        Collections.sort(someStringList, new Comparator<String>() {
            @Override
            public int compare(String s1, String s2) {
                return theNodesDistance(s1).compareTo(theNodesDistance(s2));
            }

        });
        System.out.println(someStringList);

    }
    public static Integer theNodesDistance(String str){
        return Integer.parseInt(str); // here return the distance
    }

Another option is to create a class Node with an id and distance:

public class Node implements Comparable<Node> {

    String id;
    Integer distance;

    public Node(String id) {
        this.id = id;
        this.distance = theNodesDistance(id);
    }

    @Override
    public int compareTo(Node node) {
        return this.distance.compareTo(node.distance);
    }

    public String toString() {
        return id;
    }

    public Integer theNodesDistance(String str){
        return Integer.parseInt(str);
    }
}

Then, sort your list doing:

LinkedList<Node> nodes = new LinkedList<>();

nodes.add(new Node("2"));
nodes.add(new Node("1"));

System.out.println(nodes);

Collections.sort(nodes);
System.out.println(nodes);

Finally, you can use a PriorityQueue which organizes the elements whenever you insert a new node. I mean, you can remove each node in order.

Queue<Node> nodes = new PriorityQueue<>();
nodes.add(new Node("10"));
nodes.add(new Node("3"));
nodes.add(new Node("2"));
nodes.add(new Node("1"));
nodes.add(new Node("4"));

System.out.println(nodes.remove());
System.out.println(nodes.remove());
System.out.println(nodes.remove());
System.out.println(nodes.remove());
System.out.println(nodes.remove());

In this case, the output will be:

1
2
3
4
10

Answer 2

If you can afford to waste CPU in repeated calculations of the distance, then you could use the JDK sorting methods with a Comparator implementation which would figure the distance from any 2 strings and compare them. This is the simplest.

If you would prefer calculating only once the distance for each string (presuming this is costly), then you either:

a) construct a new collection of tuples (string and distance), and sort the tuples by the distance (again with a comparator, or by making the tuple class comparable).

b) or you can try to cache the distances in a hashmap of strings-to-distance which the comparator would rely on.

Answer 3

You can use TreeMap.. Following is a normal demonstration -

    TreeMap<Integer, String> tmap = new TreeMap<Integer, String>(); 
/*Adding elements to TreeMap*/
 tmap.put(1, "Data1"); 
tmap.put(23, "Data2"); 
tmap.put(70, "Data3"); 
tmap.put(4, "Data4"); 
tmap.put(2, "Data5"); 
/* Display content using Iterator*/ 
Set set = tmap.entrySet();
 Iterator iterator = set.iterator();
 while(iterator.hasNext()) { 
Map.Entry mentry = (Map.Entry)iterator.next();
 System.out.print("key is: "+ mentry.getKey() + " & Value is: ");
 System.out.println(mentry.getValue()); 
} 

The output ::

key is: 1 & Value is: Data1 
key is: 2 & Value is: Data5 
key is: 4 & Value is: Data4 
key is: 23 & Value is: Data2 
key is: 70 & Value is: Data3

Answer 4

You can use sort algo. like selectionsort, bubblesort... This is insertionsort

double temp;
for(int i = 1;i<yourList.size();i++)
{
temp = thenodedistance(yourlist.get(i));
int j = i;
    while(j>0&&thenodedistance(yourlist.get(j-1))> temp)
    {
        yourlist.add(j,yourlist.remove(j-1);
        j--;
    }
    yourlist.add(j,yourliste.remove(i));
}

this way you can sort your list (did not try the code....)

Answer 5

What about having a Node class?

class Node{
   String str;
   int distance;
   public Node(String str){
       this.str = str;
       this.distance = theNodesDistance(str);
   }
}

Then you can override a Comparator. I suggest you to use a PriorityQueue instead of a LinkedList so your inserts to the ordered list can be more efficient (O(logn)). In this case you dont really need to call a sort or heapify function since the priority queue always keeps the nodes in order.

PriorityQueue que = new PriorityQueue(new Comparator<Node>(){
     public int compare(Node n1, Node n2){
          if(n1.distance < n2. distance) return -1;
          else if(n1.distance > n2.distance) return 1;
          return 0;
     }
});

You can add to the que as follows:

for(each str){
    que.add(new Node(str));
}