算法Sedgewick第四版-第1章基础-011一用链表实现bag、queue、stack

1.

package algorithms.ADT;

/******************************************************************************
 *  Compilation:  javac Bag.java
 *  Execution:    java Bag < 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 Bag < tobe.txt
 *  size of bag = 14
 *  is
 *  -
 *  -
 *  -
 *  that
 *  -
 *  -
 *  be
 *  -
 *  to
 *  not
 *  or
 *  be
 *  to
 *
 ******************************************************************************/

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

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

/**
 *  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>
 *  This implementation uses a singly-linked list with a static nested class Node.
 *  See {@link LinkedBag} for the version from the
 *  textbook that uses a non-static nested class.
 *  The <em>add</em>, <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
 *
 *  @param <Item> the generic type of an item in this bag
 */
public class Bag<Item> implements Iterable<Item> {
    private Node<Item> first;    // beginning of bag
    private int N;               // number of elements in bag

    // helper linked list class
    private static class Node<Item> {
        private Item item;
        private Node<Item> next;
    }

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

    /**
     * Returns true if this bag is empty.
     *
     * @return <tt>true</tt> if this bag is empty;
     *         <tt>false</tt> 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<Item> oldfirst = first;
        first = new Node<Item>();
        first.item = item;
        first.next = oldfirst;
        N++;
    }


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

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

        public ListIterator(Node<Item> first) {
            current = first;
        }

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

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

    /**
     * Unit tests the <tt>Bag</tt> data type.
     */
    public static void main(String[] args) {
        Bag<String> bag = new Bag<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);
        }
    }


}

 

2.

package algorithms.ADT;

/******************************************************************************
 *  Compilation:  javac Queue.java
 *  Execution:    java Queue < input.txt
 *  Dependencies: StdIn.java StdOut.java
 *  Data files:   http://algs4.cs.princeton.edu/13stacks/tobe.txt  
 *
 *  A generic queue, implemented using a linked list.
 *
 *  % java Queue < 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>Queue</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 singly-linked list with a static nested class for
 *  linked-list nodes. See {@link LinkedQueue} for the version from the
 *  textbook that uses a non-static nested class.
 *  The <em>enqueue</em>, <em>dequeue</em>, <em>peek</em>, <em>size</em>, and <em>is-empty</em>
 *  operations all take 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
 *
 *  @param <Item> the generic type of an item in this queue
 */
public class Queue<Item> implements Iterable<Item> {
    private Node<Item> first;    // beginning of queue
    private Node<Item> last;     // end of queue
    private int N;               // number of elements on queue

    // helper linked list class
    private static class Node<Item> {
        private Item item;
        private Node<Item> next;
    }

    /**
     * Initializes an empty queue.
     */
    public Queue() {
        first = null;
        last  = null;
        N = 0;
    }

    /**
     * Returns true if this queue is empty.
     *
     * @return <tt>true</tt> if this queue is empty; <tt>false</tt> otherwise
     */
    public boolean isEmpty() {
        return first == null;
    }

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

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

    /**
     * Adds the item to this queue.
     *
     * @param  item the item to add
     */
    public void enqueue(Item item) {
        Node<Item> oldlast = last;
        last = new Node<Item>();
        last.item = item;
        last.next = null;
        if (isEmpty()) first = last;
        else           oldlast.next = last;
        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 NoSuchElementException if this queue is empty
     */
    public Item dequeue() {
        if (isEmpty()) throw new NoSuchElementException("Queue underflow");
        Item item = first.item;
        first = first.next;
        N--;
        if (isEmpty()) last = null;   // to avoid loitering
        return item;
    }

    /**
     * Returns a string representation of this queue.
     *
     * @return the sequence of items in FIFO order, separated by spaces
     */
    public String toString() {
        StringBuilder s = new StringBuilder();
        for (Item item : this)
            s.append(item + " ");
        return s.toString();
    } 

    /**
     * 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 ListIterator<Item>(first);  
    }

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

        public ListIterator(Node<Item> first) {
            current = first;
        }

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

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


    /**
     * Unit tests the <tt>Queue</tt> data type.
     */
    public static void main(String[] args) {
        Queue<String> q = new Queue<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.ADT;

/******************************************************************************
 *  Compilation:  javac Stack.java
 *  Execution:    java Stack < input.txt
 *  Dependencies: StdIn.java StdOut.java
 *
 *  A generic stack, implemented using a singly-linked list.
 *  Each stack element is of type Item.
 *
 *  This version uses a static nested class Node (to save 8 bytes per
 *  Node), whereas the version in the textbook uses a non-static nested
 *  class (for simplicity).
 *  
 *  % more tobe.txt 
 *  to be or not to - be - - that - - - is
 *
 *  % java Stack < 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>Stack</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 singly-linked list with a static nested class for
 *  linked-list nodes. See {@link LinkedStack} for the version from the
 *  textbook that uses a non-static nested class.
 *  The <em>push</em>, <em>pop</em>, <em>peek</em>, <em>size</em>, and <em>is-empty</em>
 *  operations all take 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
 *
 *  @param <Item> the generic type of an item in this stack
 */
public class Stack<Item> implements Iterable<Item> {
    private Node<Item> first;     // top of stack
    private int N;                // size of the stack

    // helper linked list class
    private static class Node<Item> {
        private Item item;
        private Node<Item> next;
    }

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

    /**
     * Returns true if this stack is empty.
     *
     * @return true if this stack is empty; false otherwise
     */
    public boolean isEmpty() {
        return first == null;
    }

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

    /**
     * Adds the item to this stack.
     *
     * @param  item the item to add
     */
    public void push(Item item) {
        Node<Item> oldfirst = first;
        first = new Node<Item>();
        first.item = item;
        first.next = oldfirst;
        N++;
    }

    /**
     * Removes and returns the item most recently added to this stack.
     *
     * @return the item most recently added
     * @throws NoSuchElementException if this stack is empty
     */
    public Item pop() {
        if (isEmpty()) throw new NoSuchElementException("Stack underflow");
        Item item = first.item;        // save item to return
        first = first.next;            // delete first node
        N--;
        return item;                   // return the saved item
    }


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

    /**
     * Returns a string representation of this stack.
     *
     * @return the sequence of items in this stack in LIFO order, separated by spaces
     */
    public String toString() {
        StringBuilder s = new StringBuilder();
        for (Item item : this)
            s.append(item + " ");
        return s.toString();
    }
       

    /**
     * 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 ListIterator<Item>(first);
    }

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

        public ListIterator(Node<Item> first) {
            current = first;
        }

        public boolean hasNext() {
            return current != null;
        }

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

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


    /**
     * Unit tests the <tt>Stack</tt> data type.
     */
    public static void main(String[] args) {
        Stack<String> s = new Stack<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)");
    }
}