Java how to sort a Linked List?

Question

I am needing to sort a linked list alphabetically. I have a Linked List full of passengers names and need the passengers name to be sorted alphabetically. How would one do t

Answer 1

Elegant solution since JAVA 8:

LinkedList<String>list = new LinkedList<String>();
list.add("abc");
list.add("Bcd");
list.add("aAb");

list.sort(String::compareToIgnoreCase);

---

Another option would be using lambda expressions:

list.sort((o1, o2) -> o1.compareToIgnoreCase(o2));

Answer 2

Node mergeSort(Node head) {
    if(head == null || head.next == null) {
        return head;
    }

    Node middle = middleElement(head);
    Node nextofMiddle = middle.next;
    middle.next = null;

    Node left = mergeSort(head);
    Node right = mergeSort(nextofMiddle);

    Node sortdList = merge(left, right);

    return sortdList;
}

Node merge(Node left, Node right) {
    if(left == null) {
        return right;
    }

    if(right == null) {
        return left;
    }
    Node temp = null;
    if(left.data < right.data) {
        temp = left;
        temp.next = merge(left.next, right);
    } else {
        temp = right;
        temp.next = merge(left, right.next);
    }

    return temp;
}

Node middleElement(Node head) {
    Node slow = head;
    Node fast = head;
    while (fast != null && fast.next != null && fast.next.next != null) {
        fast = fast.next.next;
        slow = slow.next;
    }
    return slow;
}

Answer 3

In order to sort Strings alphabetically you will need to use a Collator, like:

 LinkedList<String> list = new LinkedList<String>();
 list.add("abc");
 list.add("Bcd");
 list.add("aAb");
 Collections.sort(list, new Comparator<String>() {
     @Override
     public int compare(String o1, String o2) {
         return Collator.getInstance().compare(o1, o2);
     }
 });

Because if you just call Collections.sort(list) you will have trouble with strings that contain uppercase characters.

For instance in the code I pasted, after the sorting the list will be: [aAb, abc, Bcd] but if you just call Collections.sort(list); you will get: [Bcd, aAb, abc]

Note: When using a Collator you can specify the locale Collator.getInstance(Locale.ENGLISH) this is usually pretty handy.