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Simple implementation of basic algorithm.
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/******************************************************************************
 *  Compilation:  javac LinkedBag.java
 *  Execution:    java LinkedBag < input.txt
 *  Dependencies: StdIn.java StdOut.java
 *
 *  A generic bag or multiset, implemented using a singly linked list.
 *
 *  % more tobe.txt 
 *  to be or not to - be - - that - - - is
 *
 *  % java LinkedBag < tobe.txt
 *  size of bag = 14
 *  is
 *  -
 *  -
 *  -
 *  that
 *  -
 *  -
 *  be
 *  -
 *  to
 *  not
 *  or
 *  be
 *  to
 *
 ******************************************************************************/

package edu.princeton.cs.algs4;

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

/**
 *  The {@code LinkedBag} class represents a bag (or multiset) of 
 *  generic items. It supports insertion and iterating over the 
 *  items in arbitrary order.
 *  
 *  This implementation uses a singly linked list with a non-static nested class Node.
 *  See {@link Bag} for a version that uses a static nested class.
 *  The add, isEmpty, and size operations
 *  take constant time. Iteration takes time proportional to the number of items.
 *  
 *  For additional documentation, see Section 1.3 of
 *  Algorithms, 4th Edition by Robert Sedgewick and Kevin Wayne.
 *
 *  @author Robert Sedgewick
 *  @author Kevin Wayne
 */
public class LinkedBag implements Iterable {
    private Node first;    // beginning of bag
    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 iterator()  {
        return new ListIterator();  
    }

    // an iterator over a linked list
    private class ListIterator implements Iterator {
        private Node current;

        // creates a new iterator
        public ListIterator() {
            current = first;
        }

        // is there a next item in the iterator?
        public boolean hasNext() {
            return current != null;
        }

        // 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();
            Item item = current.item;
            current = current.next; 
            return item;
        }
    }

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

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


}

/******************************************************************************
 *  Copyright 2002-2018, Robert Sedgewick and Kevin Wayne.
 *
 *  This file is part of algs4.jar, which accompanies the textbook
 *
 *      Algorithms, 4th edition by Robert Sedgewick and Kevin Wayne,
 *      Addison-Wesley Professional, 2011, ISBN 0-321-57351-X.
 *      http://algs4.cs.princeton.edu
 *
 *
 *  algs4.jar is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  algs4.jar is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with algs4.jar.  If not, see http://www.gnu.org/licenses.
 ******************************************************************************/