算法Sedgewick第四版-第1章基础-1.3Bags, Queues, and Stacks-001可变在小的

1.

package algorithms.stacks13;

/******************************************************************************
 *  Compilation:  javac ResizingArrayBag.java
 *  Execution:    java ResizingArrayBag
 *  Dependencies: StdIn.java StdOut.java
 *
 *  Bag implementation with a resizing array.
 *
 ******************************************************************************/

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

import algorithms.util.StdOut;

/**
 *  The <tt>ResizingArrayBag</tt> class represents a bag (or multiset) of
 *  generic items. It supports insertion and iterating over the
 *  items in arbitrary order.
 *  <p>
 *  This implementation uses a resizing array.
 *  See {@link LinkedBag} for a version that uses a singly-linked list.
 *  The <em>add</em> operation takes constant amortized time; the
 *  <em>isEmpty</em>, and <em>size</em> operations
 *  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.
 *
 *  @author Robert Sedgewick
 *  @author Kevin Wayne
 */
public class ResizingArrayBag<Item> implements Iterable<Item> {
    private Item[] a;         // array of items
    private int N;            // number of elements on stack

    /**
     * Initializes an empty bag.
     */
    public ResizingArrayBag() {
        a = (Item[]) new Object[2];
        N = 0;
    }

    /**
     * Is this bag empty?
     * @return true if this bag is empty; false otherwise
     */
    public boolean isEmpty() {
        return N == 0;
    }

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

    // resize the underlying array holding the elements
    private void resize(int capacity) {
        assert capacity >= N;
        Item[] temp = (Item[]) new Object[capacity];
        for (int i = 0; i < N; i++)
            temp[i] = a[i];
        a = temp;
    }

    /**
     * Adds the item to this bag.
     * @param item the item to add to this bag
     */
    public void add(Item item) {
        if (N == a.length) resize(2*a.length);    // double size of array if necessary
        a[N++] = item;                            // add item
    }

    /**
     * Returns an iterator that iterates over the items in the bag in arbitrary order.
     * @return an iterator that iterates over the items in the bag in arbitrary order
     */
    public Iterator<Item> iterator() {
        return new ArrayIterator();
    }

    // an iterator, doesn't implement remove() since it's optional
    private class ArrayIterator implements Iterator<Item> {
        private int i = 0;
        public boolean hasNext()  { return i < N;                               }
        public void remove()      { throw new UnsupportedOperationException();  }

        public Item next() {
            if (!hasNext()) throw new NoSuchElementException();
            return a[i++];
        }
    }

    /**
     * Unit tests the <tt>ResizingArrayBag</tt> data type.
     */
    public static void main(String[] args) {
        ResizingArrayBag<String> bag = new ResizingArrayBag<String>();
        bag.add("Hello");
        bag.add("World");
        bag.add("how");
        bag.add("are");
        bag.add("you");

        for (String s : bag)
            StdOut.println(s);
    }

}

2.

 package algorithms.stacks13;

 /******************************************************************************
  *  Compilation:  javac ResizingArrayQueue.java
  *  Execution:    java ResizingArrayQueue < input.txt
  *  Dependencies: StdIn.java StdOut.java
  *  Data files:   http://algs4.cs.princeton.edu/13stacks/tobe.txt
  *
  *  Queue implementation with a resizing array.
  *
  *  % java ResizingArrayQueue < tobe.txt
  *  to be or not to be (2 left on queue)
  *
  ******************************************************************************/

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

 import algorithms.util.StdIn;
 import algorithms.util.StdOut;

 /**
  *  The <tt>ResizingArrayQueue</tt> class represents a first-in-first-out (FIFO)
  *  queue of generic items.
  *  It supports the usual <em>enqueue</em> and <em>dequeue</em>
  *  operations, along with methods for peeking at the first item,
  *  testing if the queue is empty, and iterating through
  *  the items in FIFO order.
  *  <p>
  *  This implementation uses a resizing array, which double the underlying array
  *  when it is full and halves the underlying array when it is one-quarter full.
  *  The <em>enqueue</em> and <em>dequeue</em> operations take constant amortized time.
  *  The <em>size</em>, <em>peek</em>, and <em>is-empty</em> operations takes
  *  constant time in the worst case.
  *  <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.
  *
  *  @author Robert Sedgewick
  *  @author Kevin Wayne
  */
 public class ResizingArrayQueue<Item> implements Iterable<Item> {
     private Item[] q;       // queue elements
     private int N;          // number of elements on queue
     private int first;      // index of first element of queue
     private int last;       // index of next available slot

     /**
      * Initializes an empty queue.
      */
     public ResizingArrayQueue() {
         q = (Item[]) new Object[2];
         N = 0;
         first = 0;
         last = 0;
     }

     /**
      * Is this queue empty?
      * @return true if this queue is empty; false otherwise
      */
     public boolean isEmpty() {
         return N == 0;
     }

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

     // resize the underlying array
     private void resize(int max) {
         assert max >= N;
         Item[] temp = (Item[]) new Object[max];
         for (int i = 0; i < N; i++) {
             temp[i] = q[(first + i) % q.length];
         }
         q = temp;
         first = 0;
         last  = N;
     }

     /**
      * Adds the item to this queue.
      * @param item the item to add
      */
     public void enqueue(Item item) {
         // double size of array if necessary and recopy to front of array
         if (N == q.length) resize(2*q.length);   // double size of array if necessary
         q[last++] = item;                        // add item
         if (last == q.length) last = 0;          // wrap-around
         N++;
     }

     /**
      * Removes and returns the item on this queue that was least recently added.
      * @return the item on this queue that was least recently added
      * @throws java.util.NoSuchElementException if this queue is empty
      */
     public Item dequeue() {
         if (isEmpty()) throw new NoSuchElementException("Queue underflow");
         Item item = q[first];
         q[first] = null;                            // to avoid loitering
         N--;
         first++;
         if (first == q.length) first = 0;           // wrap-around
         // shrink size of array if necessary
         if (N > 0 && N == q.length/4) resize(q.length/2);
         return item;
     }

     /**
      * Returns the item least recently added to this queue.
      * @return the item least recently added to this queue
      * @throws java.util.NoSuchElementException if this queue is empty
      */
     public Item peek() {
         if (isEmpty()) throw new NoSuchElementException("Queue underflow");
         return q[first];
     }

     /**
      * Returns an iterator that iterates over the items in this queue in FIFO order.
      * @return an iterator that iterates over the items in this queue in FIFO order
      */
     public Iterator<Item> iterator() {
         return new ArrayIterator();
     }

     // an iterator, doesn't implement remove() since it's optional
     private class ArrayIterator implements Iterator<Item> {
         private int i = 0;
         public boolean hasNext()  { return i < N;                               }
         public void remove()      { throw new UnsupportedOperationException();  }

         public Item next() {
             if (!hasNext()) throw new NoSuchElementException();
             Item item = q[(i + first) % q.length];
             i++;
             return item;
         }
     }

    /**
      * Unit tests the <tt>ResizingArrayQueue</tt> data type.
      */
     public static void main(String[] args) {
         ResizingArrayQueue<String> q = new ResizingArrayQueue<String>();
         while (!StdIn.isEmpty()) {
             String item = StdIn.readString();
             if (!item.equals("-")) q.enqueue(item);
             else if (!q.isEmpty()) StdOut.print(q.dequeue() + " ");
         }
         StdOut.println("(" + q.size() + " left on queue)");
     }

 }

3.

 package algorithms.stacks13;

 /******************************************************************************
  *  Compilation:  javac ResizingArrayStack.java
  *  Execution:    java ResizingArrayStack < input.txt
  *  Dependencies: StdIn.java StdOut.java
  *  Data files:   http://algs4.cs.princeton.edu/13stacks/tobe.txt
  *
  *  Stack implementation with a resizing array.
  *
  *  % more tobe.txt
  *  to be or not to - be - - that - - - is
  *
  *  % java ResizingArrayStack < tobe.txt
  *  to be not that or be (2 left on stack)
  *
  ******************************************************************************/

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

 import algorithms.util.StdIn;
 import algorithms.util.StdOut;

 /**
  *  The <tt>ResizingArrayStack</tt> class represents a last-in-first-out (LIFO) stack
  *  of generic items.
  *  It supports the usual <em>push</em> and <em>pop</em> operations, along with methods
  *  for peeking at the top item, testing if the stack is empty, and iterating through
  *  the items in LIFO order.
  *  <p>
  *  This implementation uses a resizing array, which double the underlying array
  *  when it is full and halves the underlying array when it is one-quarter full.
  *  The <em>push</em> and <em>pop</em> operations take constant amortized time.
  *  The <em>size</em>, <em>peek</em>, and <em>is-empty</em> operations takes
  *  constant time in the worst case.
  *  <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.
  *
  *  @author Robert Sedgewick
  *  @author Kevin Wayne
  */
 public class ResizingArrayStack<Item> implements Iterable<Item> {
     private Item[] a;         // array of items
     private int N;            // number of elements on stack

     /**
      * Initializes an empty stack.
      */
     public ResizingArrayStack() {
         a = (Item[]) new Object[2];
         N = 0;
     }

     /**
      * Is this stack empty?
      * @return true if this stack is empty; false otherwise
      */
     public boolean isEmpty() {
         return N == 0;
     }

     /**
      * Returns the number of items in the stack.
      * @return the number of items in the stack
      */
     public int size() {
         return N;
     }

     // resize the underlying array holding the elements
     private void resize(int capacity) {
         assert capacity >= N;
         Item[] temp = (Item[]) new Object[capacity];
         for (int i = 0; i < N; i++) {
             temp[i] = a[i];
         }
         a = temp;
     }

     /**
      * Adds the item to this stack.
      * @param item the item to add
      */
     public void push(Item item) {
         if (N == a.length) resize(2*a.length);    // double size of array if necessary
         a[N++] = item;                            // add item
     }

     /**
      * Removes and returns the item most recently added to this stack.
      * @return the item most recently added
      * @throws java.util.NoSuchElementException if this stack is empty
      */
     public Item pop() {
         if (isEmpty()) throw new NoSuchElementException("Stack underflow");
         Item item = a[N-1];
         a[N-1] = null;                              // to avoid loitering
         N--;
         // shrink size of array if necessary
         if (N > 0 && N == a.length/4) resize(a.length/2);
         return item;
     }

     /**
      * Returns (but does not remove) the item most recently added to this stack.
      * @return the item most recently added to this stack
      * @throws java.util.NoSuchElementException if this stack is empty
      */
     public Item peek() {
         if (isEmpty()) throw new NoSuchElementException("Stack underflow");
         return a[N-1];
     }

     /**
      * Returns an iterator to this stack that iterates through the items in LIFO order.
      * @return an iterator to this stack that iterates through the items in LIFO order.
      */
     public Iterator<Item> iterator() {
         return new ReverseArrayIterator();
     }

     // an iterator, doesn't implement remove() since it's optional
     private class ReverseArrayIterator implements Iterator<Item> {
         private int i;

         public ReverseArrayIterator() {
             i = N-1;
         }

         public boolean hasNext() {
             return i >= 0;
         }

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

         public Item next() {
             if (!hasNext()) throw new NoSuchElementException();
             return a[i--];
         }
     }

     /**
      * Unit tests the <tt>Stack</tt> data type.
      */
     public static void main(String[] args) {
         ResizingArrayStack<String> s = new ResizingArrayStack<String>();
         while (!StdIn.isEmpty()) {
             String item = StdIn.readString();
             if (!item.equals("-")) s.push(item);
             else if (!s.isEmpty()) StdOut.print(s.pop() + " ");
         }
         StdOut.println("(" + s.size() + " left on stack)");
     }
 }