LinkedList manipulations.

LinkedListHelper.cs

public class LinkedListNode
{
    public int val;
    public LinkedListNode next;
}

public class LinkedListHelper
{
    public static LinkedListNode MergeLinkedLists(LinkedListNode head1, LinkedListNode head2)
    {
        if (head1 == head2 == null)
        {
            return null;
        }

        if (head1 == null)
        {
            return head2;
        }

        if (head2 == null)
        {
            return head1;
        }

        if (head1.val >= head2.val)
        {
            head1 = new LinkedListNode { val = head2.val, next = head1 };
            head1.next = MergeLinkedLists(head1.next, head2.next);
        }
        else
        {
            head1.next = MergeLinkedLists(head1.next, head2);
        }

        return head1;
    }

    public static LinkedListNode RemoveInteger(LinkedListNode head, int intToRemove)
    {
        if (head == null)
        {
            return null;
        }

        while (head.val == intToRemove)
        {
            head = head.next;
        }

        if (head.next != null)
        {
            head.next = RemoveInteger(head.next, intToRemove);
        }

        return head;
    }

    public static LinkedListNode InsertInteger(LinkedListNode head, int intToInsert)
    {
        if (head == null)
        {
            return null;
        }

        if (head.val > intToInsert)
        {
            return new LinkedListNode { val = intToInsert, next = head };
        }

        if (head.next == null)
        {
            head.next = new LinkedListNode { val = intToInsert };
        }
        else if (head.next.val >= intToInsert)
        {
            var nextToMove = head.next;
            head.next = new LinkedListNode { val = intToInsert, next = nextToMove };
        }
        else
        {
            head.next = InsertInteger(head.next, intToInsert);
        }

        return head;
    }
}