问题
I have here a single linked list for a program that makes a collage. This runs perfectly but I was wondering how to make it a double linked list. I really have no idea what a double linked is though or how to create one. Any help would be appreciated...
There are 3 classes.
class LinearCollage
{
private Picture myArray[];
private class Node
{
Picture data;
Node pNext;
};
private Node pFirst;
private Node pLast;
private int nPictures;
private Picture clipboard;
public LinearCollage()
{
pFirst = null;
pLast = null;
nPictures = 0;
}
public void addPictureAtEnd(Picture aPictureReference)
{
Node temp = new Node();
temp.data = aPictureReference;
temp.pNext = null;
if( pLast == null )
{
pLast = temp;
pFirst = temp;
}
else
{
pLast.pNext = temp;
pLast = temp;
}
nPictures++;
}
public Picture makeCollage()
{
int collageHeight = 400;
int collageWidth = 400;
for( Node finger = pFirst; finger != null; finger = finger.pNext )
{
System.out.println("Process Picture " + finger.data);
}
Picture retval = new Picture(collageHeight,collageWidth);
int i = 0;
for( Node finger = pFirst; finger != null; finger = finger.pNext )
{
System.out.println("Process Picture " + finger.data);
finger.data.compose(retval, 50*i, 50*i);
i++;
}
return retval;
}
public void cutMiddle()
{
int cutIndex = nPictures-1;
clipboard = myArray[cutIndex];
for( int i = cutIndex; i < nPictures - 1; i++ )
{
myArray[i] = myArray[i + 1];
}
nPictures--;
}
public void cutEnd()
{
int cutIndex = nPictures;
clipboard = myArray[cutIndex];
for( int i = cutIndex; i<nPictures - 1; i++)
{
myArray[i] = myArray[i + 1];
}
nPictures--;
}
public void pasteEnd()
{
myArray[nPictures] = clipboard;
nPictures++;
}
public boolean isFull()
{
return false;
}
public boolean isEmpty()
{
return nPictures == 0;
}
}
import java.util.Scanner;
class LineCollageMaker
{
public static void main(String a[])
{
LinearCollage myCollage;
Scanner uiInput = new Scanner(System.in);
myCollage = new LinearCollage();
FileChooser.pickMediaPath();
boolean inputting = true;
while( inputting )
{
System.out.println("Another picture? Type Y if so.");
String answer = uiInput.next();
if(answer.equals("Y"))
{
Picture pin = new Picture(FileChooser.pickAFile());
myCollage.addPictureAtEnd(pin);
}
else
{
inputting = false;
}
}
Picture firstToShow = myCollage.makeCollage();
firstToShow.show();
//YOU Code the user inteface loop and dispatch to methods
//of myCollage here..
boolean done = false;
while( !done )
{
System.out.println("MENU (CASE SENSITIVE!)");
System.out.println("CM - cut middle and move it to the clipboard");
System.out.println("PE - paste clipboard to end");
System.out.println("CE - cut end and move it to clipboard");
System.out.println("XX - stop running this program");
String command = uiInput.next();
if(command.equals("XX"))
done = true;
else if(command.equals("CM"))
{
if(myCollage.isEmpty())
{
System.out.println("Can't cut from an empty collage.");
}
else
{
myCollage.cutMiddle();
myCollage.makeCollage().show();
}
}
else if(command.equals("PE"))
{
if(myCollage.isFull())
{
System.out.println("Can't paste to an empty collage.");
}
else
{
myCollage.pasteEnd();
myCollage.makeCollage().show();
}
}
else if(command.equals("CE"))
{
if(myCollage.isEmpty())
{
System.out.println("Can't copy from an empty collage.");
}
else
{
myCollage.cutEnd();
myCollage.makeCollage().show();
}
}
else
System.out.println("Unrecognized command. Try again.");
}
}
}
public class Node
{
//le class variables
private Picture myPic;
private Node next;
//le constructors
public Node(Picture heldPic)
{
myPic=heldPic;
next=null;
}
public void setNext(Node nextOne)
{
this.next=nextOne;
}
public Node getNext()
{
return this.next;
}
public Picture getPicture()
{
return this.myPic;
}
//le methods
public void drawFromMeOn(Picture bg)
{
Node current;
int currentX=0, currentY=bg.getHeight()-1;
current = this;
while (current != null)
{
current.drawMeOn(bg,currentX, currentY);
currentX = currentX + current.getPicture().getWidth();
current=current.getNext();
}
}
private void drawMeOn(Picture bg, int left, int bottom)
{
this.getPicture().blueScreen(bg, left, bottom-this.getPicture().getHeight());
}
}
回答1:
A doubly linked list is simply a linked list where every element has both next and prev mebers, pointing at the elements before and after it, not just the one after it in a single linked list.
so to convert your list to a doubly linked list, just change your node to be:
private class Node
{
Picture data;
Node pNext;
Node pPrev;
};
and when iterating the list, on each new node add a reference to the previous node.
回答2:
A doubly-linked list takes a singly-linked list one step further by also having a reference to the previous node, rather than just the next one.
I confess I am slightly confused by your code as it looks like you have a private class for Node and then another public class for it. To make this a doubly-linked list add another Node instance variable into your Node class which references the previous node, and then update this variable when you add in new nodes.
回答3:
You can convert Single linked list to Double linked list via a concept called XOR based linked list. The beauty of XOR truth table makes suitable for this use case.
Check this out : https://www.geeksforgeeks.org/xor-linked-list-a-memory-efficient-doubly-linked-list-set-1/
来源：https://stackoverflow.com/questions/9542154/converting-a-single-linked-list-to-a-double-linked-list