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package algs13;
import  stdlib.*;

/* ***********************************************************************
 *  Compilation:  javac Bag.java
 *  Execution:    java Bag < input.txt
 *
 *  A generic bag or multiset, implemented using a linked list.
 *
 *  % more tobe.txt
 *  to be or not to - be - - that - - - is
 *
 *  % java Bag < tobe.txt
 *  size of bag = 14
 *  is
 *  -
 *  -
 *  -
 *  that
 *  -
 *  -
 *  be
 *  -
 *  to
 *  not
 *  or
 *  be
 *  to
 *
 *************************************************************************/

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

/**
 *  The <tt>Bag</tt> class represents a bag (or multiset) of
 *  generic items. It supports insertion and iterating over the
 *  items in arbitrary order.
 *  <p>
 *  The <em>add</em>, <em>isEmpty</em>, and <em>size</em>  operation
 *  take constant time. Iteration takes time proportional to the number of items.
 *  <p>
 *  For additional documentation, see <a href="http://algs4.cs.princeton.edu/13stacks">Section 1.3</a> of
 *  <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
 */
public class Bag<T> implements Iterable<T> {
  private int N;         // number of elements in bag
  private Node<T> first;    // beginning of bag

  // helper linked list class
  private static class Node<T> {
    public Node() { }
    public T item;
    public Node<T> next;
  }

  /**
   * Create an empty stack.
   */
  public Bag() {
    first = null;
    N = 0;
  }

  /**
   * Is the BAG empty?
   */
  public boolean isEmpty() {
    return first == null;
  }

  /**
   * Return the number of items in the bag.
   */
  public int size() {
    return N;
  }

  /**
   * Add the item to the bag.
   */
  public void add(T item) {
    Node<T> oldfirst = first;
    first = new Node<>();
    first.item = item;
    first.next = oldfirst;
    N++;
  }

  // check internal invariants
  protected static <T> boolean check(Bag<T> that) {
    int N = that.N;
    Bag.Node<T> first = that.first;
    if (N == 0) {
      if (first != null) return false;
    }
    else if (N == 1) {
      if (first == null)      return false;
      if (first.next != null) return false;
    }
    else {
      if (first.next == null) return false;
    }

    // check internal consistency of instance variable N
    int numberOfNodes = 0;
    for (Bag.Node<T> x = first; x != null; x = x.next) {
      numberOfNodes++;
    }
    if (numberOfNodes != N) return false;

    return true;
  }


  /**
   * Return an iterator that iterates over the items in the bag.
   */
  public Iterator<T> iterator()  {
    return new ListIterator();
  }

  // an iterator, doesn't implement remove() since it's optional
  private class ListIterator implements Iterator<T> {
    private Node<T> current = first;

    public boolean hasNext()  { return current != null;                     }
    public void remove()      { throw new UnsupportedOperationException();  }

    public T next() {
      if (!hasNext()) throw new NoSuchElementException();
      T item = current.item;
      current = current.next;
      return item;
    }
  }

  /**
   * A test client.
   */
  public static void main(String[] args) {
    StdIn.fromString ("to be or not to - be - - that - - - is");
    Bag<String> bag = new Bag<>();
    while (!StdIn.isEmpty()) {
      String item = StdIn.readString();
      bag.add(item);
    }

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