package linkedLists;

public class DIntList {
	/** Doubly linked list with just a head, storing Integers*/
	//contains recursive methods
		private DIntNode head;  //head node of the list
		
		/** Default constructor that creates an empty list */
		public DIntList(){
			head=null;
		}
		
		//note new constructor here, to help with recursion
		/**constructor to create a list with head node n*/
		public DIntList(DIntNode n){
			head=n;
			if (head!=null) head.setPrev(null);
		}
		
		
		/**return the head of the list*/
		public DIntNode getHead(){
			return head;
		}
		
		/**set the head of the list*/
		public void setHead(DIntNode n){
			head=n;
		}
		
		/**is the list empty?*/
		public boolean isEmpty(){
			return(head==null);
		}
		
		/**add a new node at front of list */
		public void addFirst(DIntNode n){
			n.setNext(head);
			if(head!=null) head.setPrev(n);
			head=n;
		}
		
		
		
		/** add node to front of list containing a given value */
		public void addValue(int i){
			DIntNode temp = new DIntNode(i,null,null);
			addFirst(temp);
			
		}
		
		
		
	   
		
		/**output positive elements of list*/
		public void writePos(){
			if (!isEmpty()){
				if(head.getElement()>0) System.out.print(head.getElement()+" ");
				DIntList myList=new DIntList(head.getNext());
				myList.writePos();
			}
		}
		
		/**delete the first node containing 0 from list
		 * and return the head of the list
		 */
		public DIntNode delete0(){
			if(!isEmpty()){
				if (head.getElement()==0) {head=head.getNext();return head;}
				else{
					DIntList myList=new DIntList(head.getNext());
					DIntNode temp = myList.delete0();
				    head.setNext(temp);
				    if (temp!=null) temp.setPrev(head);
				    return head;
				    }
			}
			else return null;
		}
		
		/**delete all nodes containing the value v from list
		 * and return the head of the list
		 */
		public DIntNode delete(int v){
			if(!isEmpty()){
				if (head.getElement()==v){
					head=head.getNext();
					return delete(v);}
				else{
				DIntList myList=new DIntList(head.getNext());
				DIntNode temp=myList.delete(v);
			    head.setNext(temp);
			    if (temp!=null) temp.setPrev(head);
			    return head;
			    }
			}
			else return null;
		}
		
		
		
		
		/**return size of list*/
		public int size(){
			if(isEmpty()) return 0;
			DIntList tempList=new DIntList(head.getNext());
			return(1+tempList.size());
			}
		
		/**returns the sum of the elements list, recursive*/
		public int sum(){
			if(head==null) return 0;
			// note didnt use an else here as program stops on reaching return
			DIntList tempList=new DIntList(head.getNext());
			return(head.getElement()+ tempList.sum());
		}
		
		/** String representation of list, recursive */
		public String toString(){
			DIntList myList;
			if (isEmpty()) return "";
			else{myList=new DIntList(head.getNext());
			     return (head.getElement()+" " + myList.toString());
			}
		}
	}