按升序打印自定义链接列表的元素

Question

I'm relatively new to Java and trying to learn on my free-time before I start taking on bigger data structures. Tonight its all about the Linked List. I have a LinkedList and trying to put the list in ascending order. Say we have numbers 5, 4, 6, 9, 1.

How would you write a method - to actually make it 1, 4, 5, 6, 9?

Right now, I'm currently trying to do this and all I'm having is:

public void order (LinkedList head) {
    if (head == null)
      return;
    else {
      order(head.next);
      System.out.print(" " + head.data);
      return;

Instead of ascending order its printing out the reverse of the original linked list: 1, 9, 6, 4, 5.

What am I doing wrong here?

Answer 1

If LinkedList is a class defined by yourself, either you

1) Write your own sort method to perform sort or

2) Let your Node class from which forms up your LinkedList to implement Comparable . Create an ArrayList and add the nodes into it. After that you will be able to sort it with Collections.sort(yourNewArrayList) .

You will have something like:

public class Node implements Comparable<Node>{
    private int value;
    //constructor, getters and other members not shown

    @Override
    public int compareTo(Node n){
        return this.getValue() - n.getValue();
    }
}

ArrayList list<Node> = new ArrayList<Node>();
while(linkedList.hasNext()){
    list.add(linkedList.next());
}

Collections.sort(list);

It is also worth taking note that the sort implemented by Java uses Dual-Pivot Quicksort which gives you O(n(log n) performance.

Answer 2

You have two choices here, depending on your goals:

1. For code that works, use java.util.LinkedList or java.util.ArrayList and java.util.Collections.sort() . These are written by very good programmers and used all of the time by millions of programmers around the world. So you do not have to worry about bugs and can get to work on writing something useful.

2. If you are interested in learning the nuts and bolts of data structures, it appears that you have already written your own LinkedList class. Now you need to write your own sort() method. Sorting is a very well understood problem and there are many online resources available that explain different sorting algorithms. These are good learning tools because there are so many variations with different strengths and weaknesses.