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Thread: Sorted Doubly linked List

  1. #1
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    Default Sorted Doubly linked List

    I required to create a sorted doubly linked list for my homework. Inside the SortedStringList, I need to implement a method called insert(). I have some problem in doing so. I don't what is going wrong to my code below:



    public class SortedStringList {
     
       private static class Node {
        public String value;
        public Node previous, next;
     
        public Node(String v, Node p, Node n) {
            value = v;
            previous = p;
            next = n;
        }
    }
     
    private Node first;
    private Node last;
     
    public SortedStringList(){
        this.first = null;
        this.last = null;
    }
     
    public void insert(String s){
        Node newnode = new Node(s,this.first,this.last);
        if(first == null){
            first = newnode;
        }
     else
         if(first.value.compareTo(s) >= 0){
             newnode.next = first;
             newnode.previous = null;
             first = newnode;
             last = first;
         }
     else
         {
            Node current = first;
            newnode.previous = first;
     
            while(current.value.compareTo(s)<=0 ){
                if(current.next == null){
                    current.next = newnode;
                    first = current;
                    last = newnode.next;
     
                }
                first.previous = current;
                current = current.next;
            }
                first.previous.next = newnode;
                newnode.next = current;
                current = first;
     }
     
     
     
    }
    }



    Can somebody please give me some idea?


  2. #2
    Member Darryl.Burke's Avatar
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    Default Re: Sorted Doubly linked List

    Cross posted
    Sorted Doubly linked List - Java Forums

    Any more?

    db

  3. #3
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    Default Re: Sorted Doubly linked List

    package Assignment4;
     
    import javax.swing.JOptionPane;
     
    // this class basically just sorts the DoublyLinkedList it has internally.  
     
    /**
     * @author pradcoc
     *
     */
    public class SortedDoublyLinkedList<T extends Comparable> {
     
    	private DoublyLinkedList<T> dll;
     
    	public SortedDoublyLinkedList()
    	{
    		dll = new DoublyLinkedList<T>();
    	}
     
     
    	public void add(T data)
    	{
    		for (int penguin = 0; penguin < dll.Size(); penguin++)
    		{
     
    			// adds it when it is "less than" the next value
    			if (data.compareTo(dll.get(penguin)) == -1)
    			{
    				dll.add(penguin, data);
    			}
     
    			// also adds it, because I don't quite know what to do with equal values, when its next value is equal to it
    			else if (data.compareTo(dll.get(penguin)) == 0)
    			{
    				dll.add(penguin, data);
    			}
     
    			else
    			{
    				// if its next value is not the maximum, it does nothing and keeps going
    				if (penguin != dll.Size() -1)
    				{
    					// don't add it
    				}
    				// when it reaches the end it adds it
    				else
    					dll.add(penguin, data);
    			}
    		}
    	}
    	public String toString()
    	{
     
    		return(dll.toString());
    	}
     
    	public void removeLast()
    	{
    		/* String str = "["
    			String str
    		for (int j = 0; j < dll.Size(); j++)
    		{
    			dll.get(j).compareTo(dll.get(j+1));
     
     
    		}
    		*/
    		if (dll.Size() == 0)
    		{
    			JOptionPane.showMessageDialog(null, "Cannot remove from an empty list!", "Invalid removal", JOptionPane.ERROR_MESSAGE);
    			return;
    		}
    		dll.removeLast();
    	}
     
    	public void removeFirst()
    	{
    		dll.removeLast();
    	}
     
    }

    package Assignment4;
     
    import javax.swing.Icon;
    import javax.swing.ImageIcon;
    import javax.swing.JOptionPane;
    import java.util.*;
    import java.io.*;
    //Paul Adcock
    // Assignment 4
    // Lasted Worked On: 10/12/2010
     
    // this class is the Doubly Linked list class.  It has a Node that holds a reference to some date of type T and has a reference
    // to the next Node and to the previous Node.  
     
     
    public class DoublyLinkedList<T>
    {
        private class Node<T>
        {
            private T data;
            private Node<T> next;
                   private Node<T> previous;
     
            public Node(T data,Node<T> next, Node<T> previous)
            {
                this.data = data;
                this.next = next;
                           this.previous=previous;
            }
     
            public T getData()
            {
                return data;
            }
     
            public Node<T> getNext()
            {
                return next;
            }
     
    public Node<T> getPrevious()
    {
    return previous;
    }
     
            public void setNext(Node<T> next)
            {
                this.next = next;
            }      
     
    public void setPrevious(Node<T> previous)
    {
    this.previous = previous;
    }
        }
     
        private Node<T> head;//head of the linked list
           private Node<T> tail; // tail of linked list
        private int size;
       private ImageIcon icon;
       private Icon icon2;
        public DoublyLinkedList()
        {
            head = null;
                    tail = null;
            size = 0;
            icon = new ImageIcon("doh3.jpg");
        }
     
        // returns a String of all the items in the linked list.  
        public String toString()
        {
            String str = "[";
     
            Node<T> curr;
     
            for (curr=head;curr!=null;curr = curr.getNext())
            {
                str = str + curr.getData();
                if (curr.getNext()!=null)
                    str = str + " ";
            }
            str = str + "]";
            return str;
     
     
        }
     
        // adds the data as the first element.  If the list size is 0, makes first element tail.  If head is not null, it puts the old
        // tail as the second element and the new element as the new head.  
        public void addFirst(T data)
    {  
        /*  Since this is the first Object,  previous should be null
         */
        Node<T> newNode = new Node<T>(data,head,null);
        //We know that if head is null, the list is empty
        if (head==null)
            {
            //If the list is empty,  tail will be newNode
            tail = newNode;
        }
     
        if(head!=null)
            head.setPrevious(newNode);
     
        //We want to set head to be newNode
    // if the list was empty before, both head and tail will be set to newNode;
        head = newNode;
        //Increment Size
        size++;
    }
     
        public void removeFirst()
        {
               if (size == 0)
    {
            	   JOptionPane pane = new JOptionPane();
            	   pane.setIcon(icon);
    pane.showMessageDialog(null, "Cannot remove from an empty list!", "Invalid removal", JOptionPane.ERROR_MESSAGE);
    pane.setMessageType(JOptionPane.ERROR_MESSAGE);
     
    return;
    }
            Node<T> current = head; // creates a Node called current and sets it to head.
     
            head = head.getNext(); //move head to the next element
     
            current.setNext(null);
    size--;
        }
     
        public void addLast(T data)
        {
            //If there are no elements, use the addFirst method
            if (tail == null)
            {
                addFirst(data);
                return;
            }
            /* Create the new Node from the data. Set next to null
             * because this will be the last element and will not
             * have a next. Set previous to tail because tail has
             * not been changed yet and is currently referencing
             * that element that will be directly before this element
             */
            Node<T> newNode = new Node(data,null,tail);
            /* Since the tail variable still references the element
             * directly before the new element, we can set that node's
             * next to our new element.
             */
            tail.setNext(newNode);
            //Set tail to our new Node
            tail = newNode;
            //Increment size
            size++;
        }
     
        public int Size()
        {
        	return(size);
        }
     
        public void add(int index,T data)
        {
            int i;
           if (index == 0)
           {
        	   addFirst(data);
        	   return;
     
           }
            if (index>size)
            {
            	JOptionPane.showMessageDialog(null, "Cannot add out of bounds!", "Invalid command", JOptionPane.ERROR_MESSAGE);
            	return;
            }
     
     
            if (index < 0)
            {
            	JOptionPane.showMessageDialog(null, "Cannot add out of bounds!", "Invalid command", JOptionPane.ERROR_MESSAGE);
            	return;
            }
     
            if (head==null)
            {
                addFirst(data);
                return;
            }
     
            if (index == size)
            {
            	addLast(data);
            	return;
            }
     
            //step 1
            Node<T> current;
     
            current = head;
     
            for (i=0;i<index-1;i++)
            {
                current = current.getNext();
            }
     
            //current now refers to object immediately before new node
     
            //step 2
            Node<T> newnode = new Node<T>(data,current.getNext(), current.getPrevious());
     
            //step 3
     
            current.setNext(newnode);
     
     
            size++;
        }  
     
        public void remove(int index)
        {
            if ((index<0) || (index>=size))
    {
    JOptionPane.showMessageDialog(null, "You cannot remove an out-of-bounds value!", "Invalid removal", JOptionPane.ERROR_MESSAGE);
                return;
            }
            Node<T> current,previous2;
     
            current = head; // makes current equal to head
            previous2 = null;
     
            for (int i=0;i<index;i++)
            {
                previous2 = current;
                current = current.getNext();
            }
           // for remove(3)
            // for i = 0;
            // previous2 = head;
            // current = head + 1;
            // for i = 0;
            // previous2 = head + 1;
            // current = head + 2;
            // for i = 1;
            // previous2 = head + 2;
            // current = head + 3;
            // for i = 2
            // previous2 = head + 3;
            // current = head + 4;
            // previous2.next = head + 5;
     
            Node<T> node3 = previous2;
            if (index!=0)
            {
            	  previous2.setNext(current.getNext());
     
            }
     
            else
            {
                head = head.getNext();
            }
            size--;
        }
     
        public T get(int i)
        {
        	if (i < 0 || i >= size)
        		return null;
     
        	if (i ==0)
        	{
        			Node<T> thisNode = head;
        			return(head.getData());
        	}
     
        	if (i == size - 1)
        	{
        		Node<T> thisNode = tail;
        		return(tail.getData());
        	}
        	Node<T> specialNode = head;
        	for (int x = 1; x < i + 1; x++)
        	{
        		specialNode = specialNode.getNext();
        	}
        	return(specialNode.getData());
     
        	// How do I get it to return the data at i?
     
     
        }
     
        // calls get method of first index
        public T front()
        {
        	if (head == null)
        		return null;
     
        	return(get(0));
        }
     
        // calls get Method of last index
        public T back()
        {
        	if (tail == null)
        		return null;
     
        	return(get(size - 1));
        }
     
        public void removeLast()
        {
     
        	if (head == null)
        	{
        		JOptionPane.showMessageDialog(null, "Cannot remove from an empty list!", "Invalid removal", JOptionPane.ERROR_MESSAGE);
        		return;
        	}
        	remove(Size() -1 );
        }
     
        // gets a String for the first bracket.  Then stores each set of first and last, 2nd and 2nd to last, etc, in a String array;
        // it then sets the third string to the concatination of all of the Strings in the array.  It thens puts these together and adds
        // the last set of brackets and returns the final string.  
    public String printAlternate()
    {
    /*
    This method returns a string that has
    the data in the following fashion (assume for this example that the list stores String objects)
    If the list is currently [amit is now here], it will return a string �[amit here is now]�
    If the list is currently [amit is now currently here], it will return a string �[amit here is currently now]�
    */
    	String str = "[";
    	String [] str2 = new String[size];
    for (int v = 0; v < size; v++)
    {
    	str2[v] = this.get(v) + " " + this.get(size - (v+1) );
    }
    String str3 = "";
    for (int x = 0; x < size - 2; x++)
    {
    	str3 = str2[x].concat(str2[x+1]);
    }
    String str4 = str + " " + str3 + " " + "]";
    return(str4);
    }
    }

    package Assignment4;
     
    // this is my test class
     
    public class Test {
     
    	public static void main(String[] args)
    	{
    		DoublyLinkedList<String> list= new DoublyLinkedList<String>();
    	//	list.add(0, "Mack");
    	//	System.out.println(list.get(0));
    	//	list.addFirst("Bob");
    		System.out.println(list.toString());
    		System.out.println(list.Size());
    	list.addLast("Gordon");
    	list.remove(0);
    	System.out.println(list.toString());
    	System.out.println(list.Size());
    	System.out.println(list.Size());
    	System.out.println(list.toString());
    	list.addFirst("Joe");
    	System.out.println(list.Size());
    		//list.removeFirst();
    		System.out.println(list.toString());
    	list.add(1,"Bob");
    	System.out.println(list.toString());
    	System.out.println(list.Size());
    	list.addFirst("Beth");
    	System.out.println(list.Size());
    	list.add(-1, "Mack2");
    list.get(0);
    System.out.println("Hey: " +list.get(0));
    	System.out.println(list.toString());
    	list.remove(-2);
    	list.remove(1);
    	System.out.println(list.Size());
    	System.out.println(list.toString());
    	list.removeFirst();
    	System.out.println(list.Size());
    	System.out.println(list.toString());
    	list.removeLast();
    	System.out.println(list.Size());
    	System.out.println(list.toString());
    	SortedDoublyLinkedList<String> sdll = new SortedDoublyLinkedList<String>();
    	 sdll.removeFirst();
    	System.out.println(list.toString());
    	sdll.removeFirst();
     
    	}
    }

    That's one I made for a class. Should be similar to yours.

    Maybe not exact though.

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