/******************************************************************************
 *  Name:     Kevin Wayne
 *  NetID:    wayne
 *  Precept:  P99
 *
 *  Compilation:  javac LinkedBag.java
 *  Execution:    java LinkedBag < input.txt
 *
 *  Description:  A generic bag or multiset, implemented using a singly linked list.
 ******************************************************************************/

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

public class LinkedBag<Item> implements Iterable<Item> {
    private Node first;    // first node in linked list
    private int n;         // number of elements in bag

    // helper linked-list class
    private class Node {
        private Item item;
        private Node next;
    }

    /**
     * Initializes an empty bag.
     */
    public LinkedBag() {
        first = null;
        n = 0;
    }

    /**
     * Is this bag empty?
     * @return true if this bag is empty; false otherwise
     */
    public boolean isEmpty() {
        return first == null;
    }

    /**
     * Returns the number of items in this bag.
     * @return the number of items in this bag
     */
    public int size() {
        return n;
    }

    /**
     * Adds the item to this bag.
     * @param item the item to add to this bag
     */
    public void add(Item item) {
        Node oldfirst = first;
        first = new Node();
        first.item = item;
        first.next = oldfirst;
        n++;
    }


    /**
     * Returns an iterator that iterates over the items in the bag.
     */
    public Iterator<Item> iterator()  {
        // add code here
    }

    // an iterator over a linked list
    private class ListIterator implements ____________<_____> {
        private Node current;

        // creates a new iterator
        public ListIterator() {
            // add code here
        }

        // is there a next item in the iterator?
        public boolean hasNext() {
            // add code here
        }

        // this method is optional in Iterator interface
        public void remove() {
            throw new UnsupportedOperationException();
        }

        // returns the next item in the iterator (and advances the iterator)
        public Item next() {
            if (!hasNext()) throw new NoSuchElementException();
            // add code here
        }
    }

    /**
     * Unit tests the {@code LinkedBag} data type.
     *
     * @param args the command-line arguments
     */
    public static void main(String[] args) {
        LinkedBag<String> bag = new LinkedBag<String>();
        while (!StdIn.isEmpty()) {
            String item = StdIn.readString();
            bag.add(item);
        }

        StdOut.println("size of bag = " + bag.size());
        for (String s : bag) {
            StdOut.println(s);
        }
    }


}