import java.util.Iterator;
import java.util.NoSuchElementException;

public class LinkedList<T> implements Iterable<T>{
    private ListNode<T> front;
    private int size = 0;

    public LinkedList(){
        front = null;
    }

    public void add(T obj){
        ListNode<T> node = new ListNode<T>(obj, null);
        ListNode<T> curr;

        if(front == null){
            front = node;
        }
        else{
            curr = front;

            while(curr.getNext() != null){
                curr = curr.getNext();
            }

            curr.setNext(node);
        }

        size++;
    }

    public void add(int index, T obj){
        if(index == 0){
            addFirst(obj);
        }
        else{
            ListNode<T> node = new ListNode<T>(obj, null);
            ListNode<T> curr = front;
            int c = 0;

            while(c + 1 != index && curr.getNext() != null){
                curr = curr.getNext();
                c++;
            }

            ListNode<T> next = curr.getNext();
            curr.setNext(node);
            node.setNext(next);

            size++;
        }
    }

    public void addFirst(T obj){
        front = new ListNode<T>(obj, front);
    }

    public T get(int index){
        if(front == null){
            return null;
        }
        else{
            ListNode<T> cNode = front;
            int curr = 0;

            while(cNode.getNext() != null && curr != index){
                cNode = cNode.getNext();
                curr++;
            }

            return cNode.getVal();
        }
    }

    public int size(){
        return size;
    }

    public String toString(){
        String result = "";
        ListNode<T> curr = front;

        while(curr.getNext() != null){
            result += curr.toString() + "\n";
            curr = curr.getNext();
        }

        return result;
    }

    private class Helper implements Iterator<T>{
        private int index = 0;

        public boolean hasNext(){
            return (index < size);
        }

        public void remove(){
            throw new UnsupportedOperationException();
        }

        public T next(){
            if(hasNext()){
                index++;
                return get(index);
            }
            else{
                throw new NoSuchElementException();
            }
        }
    }

    public Iterator<T> iterator(){
        return new Helper();
    }
}