DataStructuresCSharp/C#/Datastructures/LinkedList/LinkedList.cs

namespace C_.Datastructures.LinkedList
{
    public class LinkedList<T>
    {
        internal LinkedListNode<T>? Head { get; set; } = default;
        private int Count { get; set; } = 0;

        public static LinkedList<T> Create()
        {
            //Create a new empty list
            return new LinkedList<T>();
        }

        public static LinkedList<T> Create(T value)
        {
            //Create a new Class with a single item
            return new LinkedList<T>()
            {
                Head = LinkedListNode<T>.Create(value, null),
                Count = 1
            };
        }

        public static LinkedList<T> Create(LinkedList<T> list1, LinkedList<T> list2)
        {
            //Append a previous list to a new List
            LinkedList<T> list;

            list = list1;
            if (list == null || list.Count == 0) return list2;

            //Find end of list and append fist item of next list
            if (list2 == null || list.Count == 0) return list;

            LinkedListNode<T>? end = list.Traverse();
            end!.Next = list2!.Head;
            list.Count += list2!.Count;

            return list;
        }

        public T? this[int i]
        {
            get
            {
                //Check Range
                if (i >= Count || i < 0) throw new System.Exception("Error! Index out of Bounds");

                //Return Value
                LinkedListNode<T>? node = Traverse(i);
                if (node != null) return node.Value;
                return default;
            }
            set
            {
                //Check Range
                if (i >= Count || i < 0) throw new System.Exception("Error! Index out of Bounds");

                //Change Value
                LinkedListNode<T>? node = Traverse(i);
                node!.Value = value;
            }
        }

        public void Append(T value)
        {
            //Create new node
            Count++;
            LinkedListNode<T> newItem = LinkedListNode<T>.Create(value, default);

            //Set head to new item if list is empty
            if (Head == null)
            {
                Head = newItem;
                return;
            }

            //Find last item in list
            LinkedListNode<T>? end = Head;
            if (end != null)
            {
                end = Traverse();
            }

            //Append item to end
            end!.Next = newItem;
        }

        public void Insert(int index, T value)
        {
            Count++;
            if (index > Count || index < 0) throw new System.Exception("Error! Index outside of Bounds");

            //Set head to new item if list is empty
            if (index == 0 || Head == null)
            {
                Head = LinkedListNode<T>.Create(value, Head);
                return;
            }

            //Fetch point in list at which item will be added
            LinkedListNode<T>? node = Traverse(index - 1);

            node!.Next = LinkedListNode<T>.Create(value, node!.Next);
        }

        public void Delete(int index)
        {
            Count--;
            if (index > Count || index < 0) throw new System.Exception("Error! Index outside of Bounds");

            //Check if we are trying to reference the first item
            if (index == 0 && Head != default)
            {
                Head = Head!.Next;
                return;
            }

            //Find node before the one we are trying to delete and then remove / relink
            LinkedListNode<T>? node = Traverse(index - 1);

            node!.Next = node.Next!.Next;
        }

        private LinkedListNode<T>? Traverse()
        {
            //Start at Head of list
            LinkedListNode<T>? node = Head;
            if (node != null)
            {
                //continue to end of list
                while (node!.Next != default)
                {
                    node = (LinkedListNode<T>)node.Next;
                }
            }
            return node;
        }

        //private static LinkedListNode<T>? Traverse(LinkedListNode<T> start){
        //    //Start at given point in list
        //    LinkedListNode<T>? node = start;
        //    if (node != null)
        //    {
        //        //Continue to end of list
        //        while (node!.Next != default)
        //        {
        //            node = (LinkedListNode<T>)node.Next;
        //        }
        //    }
        //    return node;
        //}

        private LinkedListNode<T>? Traverse(int i)
        {
            //Start at given point in list
            LinkedListNode<T>? node = Head;
            if (node != null || i == 0)
            {
                //Continue to end of list
                for (int j = 0; j < i; j++)
                {
                    if (node!.Next == null) return null;
                    node = (LinkedListNode<T>)node.Next;
                }
            }
            return node;
        }
    }
}