C# tutorial-delete item of circularly linked list

Delete item of circularly linked list

Step 4: Delete an element of the circularly linked list

To delete an element of the circularly linked list, you need to consider the followings:

1. If the element to be deleted is the first element of the list and the list contains only one element, you only need to assign null to the pfirst and plast links. If the element to be deleted is the first element of the list and the list contain more than one element, you need a temporary link to point to the pfirst then move the pfirst to point to its next element and set the temporary link to null.

2. If the element to be deleted is in the middle of the list, you need a traversing link(temp) to point to the element before the element to be deleted and a temporary link(del) to point to the element to be deleted. Then let the next link of the traversing link to point to the next link of the temporary link. To handle situation where the element to be deleted is the last element of the list, you need to test whether the target item is equal to the plast. If it is really equal, you need to update the plast to point to the traversing link. Finally set the temporary link to null.

//C# code to  delete an item of the circularly linked list

public void delete(int pos)

            {

                int deleted = 1;

                if (pfirst != null)

                { //make sure the list is not empty.

                    ListNode<T> tr, temp;

                    if (pos == 1)

                    {//delete the first item

                        if (countitem() == 1)

                        { //The list contains only one item

                            pfirst = null;

                            plast = null;

                        }

                        else

                        { //The list contains more than one item

                            tr = pfirst;

                            pfirst = pfirst.next;

                            tr = null;

                        }

                        Console.WriteLine("Deleted");

                    }

                    else if (pos > 1 && pos <= countitem())

                    {//delete middle item

                        tr = pfirst;

                        int i;

                        for (i = 1; i < pos - 1; i = i + 1) { tr = tr.next; } //move to the item staying before the target item to be deleted

                        temp = tr.next; //target item to be deleted

                        tr.next = temp.next;

                        if (temp.next == null) plast = tr; //delete last item

                        temp = null;

                        Console.WriteLine("Deleted");

                    }

                    else { deleted = 0; Console.WriteLine("Invalid position!"); }

                    if (deleted != 0 && plast != null) plast.next = pfirst; //keep the list circularly linked

                }

                else Console.WriteLine("No item found");

            }