my assignment involves using recursive method. Write a program that reverses a LinkedList. This is the code i have done below, can anyone see what i am doing wrong, thank you very much!
PS: this is done in jGRASP
// Java program for reversing the linked list
class MyLinkedList {
static Node head;
static class Node {
int data;
Node next;
Node(int d) {
data = d;
next = null;
}
}
/* Function to reverse the linked list */
Node reverse(Node node) {
Node prev = null;
Node current = node;
Node next = null;
while (current != null) {
next = current.next;
current.next = prev;
prev = current;
current = next;
}
node = prev;
return node;
}
// prints content of double linked list
void printList(Node node) {
while (node != null) {
System.out.print(node.data + " ");
node = node.next;
}
}
public static void main(String[] args) {
MyLinkedList list = new MyLinkedList();
list.head = new Node(85);
list.head.next = new Node(15);
list.head.next.next = new Node(4);
list.head.next.next.next = new Node(20);
System.out.println("Given Linked list");
list.printList(head);
head = list.reverse(head);
System.out.println("");
System.out.println("Reversed linked list ");
list.printList(head);
}
}
Related
I am trying to delete the largest node in binary search tree, I thougth that these code below should be able to do it but for some reason it is not. Could someone help please!
public void remove() {
Node current = root;
while(true){
Node parent = current;
current = current.getRighChild();
if (current == null){
parent.setRighChild(null);
return;
}
}
}
public void remove()
{
root = deleteMax(root);
}
private Node deleteMax(Node x ) {
if (x.getRighChild() == null)
{
return x.getLeftChild();
}
x.setRighChild(deleteMax(x.getRighChild()));
return x;
}
In your code if the right node is empty you are still deleting it. Instead of deleting the current if it is the max. Try something like this:
removeLargest() {
current = getRoot();
rightNode == null;
while (root.Right){
current == root.Right
}
if (current.left()){
rotate()
}
current.delete()
}
I am using script component in ssis with C# code using Microsoft.Analysisservices namespace to fetch the cube metadata. The code looks somewhat like this
using System;
using System.Data;
using Microsoft.SqlServer.Dts.Pipeline.Wrapper;
using Microsoft.SqlServer.Dts.Runtime.Wrapper;
using Microsoft.AnalysisServices;
using System.Windows.Forms;
[Microsoft.SqlServer.Dts.Pipeline.SSISScriptComponentEntryPointAttribute]
public class ScriptMain : UserComponent
{
//IDTSConnectionManager100 connMgr;
Server OLAPServer = new Server();
public override void AcquireConnections(object Transaction)
{
OLAPServer.Connect(this.Connections.OLAPConnection.ConnectionString);
}
public override void PreExecute()
{
base.PreExecute();
/*
Add your code here for preprocessing or remove if not needed
*/
}
public override void PostExecute()
{
base.PostExecute();
/*
Add your code here for postprocessing or remove if not needed
You can set read/write variables here, for example:
Variables.MyIntVar = 100
*/
}
public override void CreateNewOutputRows()
{
IDTSVariables100 vars = null;
string OLAPDBName;
VariableDispenser.LockOneForRead("OLAPDBName", ref vars);
Database OLAPDB;
OLAPDBName = vars[0].Value.ToString();
try
{
OLAPDB = OLAPServer.Databases.GetByName(OLAPDBName);
}
catch
{
return;
}
// loop through cubes
CubeCollection Cubes = OLAPDB.Cubes;
MeasureGroupCollection Mgroups;
CubeDimensionCollection Dimensions;
MeasureGroupDimensionCollection MgroupDims;
DimensionAttributeCollection Attributes;
foreach (Cube cb in Cubes)
{
//Test for one Measure Group
//MeasureGroup mgroup = Mgroups.GetByName("Inward Exposure");
Mgroups = cb.MeasureGroups;
// all dimensions associated with that Measure Group
// loop through Measure Groups
foreach (MeasureGroup mg in Mgroups)
{
// loop though all cube dimensions
Dimensions = cb.Dimensions;**strong text**
foreach (CubeDimension dim in Dimensions)
{
bool CanBeAnalysed = false;**strong text**
// loop through dimensions and see if dimension exists in mgroupDims (ie check if it can be analysed)
MgroupDims = mg.Dimensions;
foreach (MeasureGroupDimension mgd in MgroupDims)
{
if (mgd.CubeDimension == dim)
{
CanBeAnalysed = true;
break;
}
}
// loop through each Measure and Attribute a
String DimName = dim.Name;
bool DimVisible = dim.Visible;
String MgroupName = mg.Name;
String CubeName = cb.Name;
String MeasureExpression;
String Description;
// for every attribute in dimension
Attributes = dim.Dimension.Attributes;
foreach (DimensionAttribute Attr in Attributes)
{
String AttrName = Attr.Name;
bool AttrVisible = Attr.AttributeHierarchyVisible;
String AttrNameColumn = Attr.NameColumn.ToString();
String AttributeRelationship = Attr.AttributeRelationships.ToString();
// get every measure in measuregroup
foreach (Measure m in mg.Measures)
{
String MeasureName = m.Name.ToString();
bool MeasureVisible = m.Visible;
String MeasureNameColumn = m.Source.ToString();
if (m.MeasureExpression != null)
{
// MessageBox.Show(m.MeasureExpression.ToString());
MeasureExpression = m.MeasureExpression.ToString();
}
else
{
// MessageBox.Show(m.MeasureExpression.ToString());
MeasureExpression = " " ;
}
if (m.Description != null)
{
// MessageBox.Show(m.MeasureExpression.ToString());
Description = m.Description.ToString();
}
else
{
// MessageBox.Show(m.MeasureExpression.ToString());
Description = " ";
}
Output0Buffer.AddRow();
Output0Buffer.OLAPDBName = OLAPDBName;
Output0Buffer.CubeName = CubeName;
Output0Buffer.DimensionName = DimName;
Output0Buffer.DimensionVisible = DimVisible;
Output0Buffer.AttrDDSColumn = AttrNameColumn;
Output0Buffer.AttrName = AttrName;
Output0Buffer.AttrVisible = AttrVisible;
Output0Buffer.MeasureGroupName = MgroupName;
Output0Buffer.MeasureName = MeasureName;
Output0Buffer.MeasureVisible = MeasureVisible;
Output0Buffer.MeasureDDSColumn = MeasureNameColumn;
Output0Buffer.IsAnalysable = CanBeAnalysed;
Output0Buffer.MeasureExpression = MeasureExpression;
Output0Buffer.Description = Description;
Output0Buffer.AttributeRelationship = AttributeRelationship;
}
}
} // end of Cube Dim Loop
} // end of Measure Group loop
} // end of cube loop
}
}
I was successful in getting the cube metadata with the above code.However, i am stuck at getting the metadata of the perspective cube and the Relationships of the measure groups i.e whether the measure groups are many-many. Any help is very much appreciated.
Here is some code for detecting dimension relationships including many-to-many. See the GetDimensionUsage function:
https://raw.githubusercontent.com/BIDeveloperExtensions/bideveloperextensions/master/SSAS/PrinterFriendlyDimensionUsage.cs
Here is some code around navigating perspectives:
https://raw.githubusercontent.com/BIDeveloperExtensions/bideveloperextensions/master/SSAS/TriStatePerspectivesPlugin.cs
Start reading around the following line:
if (perspective.MeasureGroups.Contains(mg.Name))
package LinkList2;
//import java.util.*;
public class Duplicates {
public static void removeDuplicates(LinkedListNode head)
{
LinkedListNode current = head;
while(current!= null && current.next!= null)
{
LinkedListNode curr = current;
while(curr!=null)
{
if(curr.next.data==current.data) //Getting error at this line
curr.next = curr.next.next;
else
curr = curr.next;
}
current = current.next;
}
}
public static void main(String args[])
{
LinkedListNode first = new LinkedListNode(0,null,null);
LinkedListNode head = first;
LinkedListNode second = first;
for(int i=1; i< 8; i++)
{
second = new LinkedListNode(i%2, null, null);
first.setNext(second);
second.setPrevious(first);
}
System.out.println(head.printForward());
removeDuplicates(head);// Getting error at this line
}
}
Getting null pointer exception in the above code. When I try to run the above code, it gives null pointer exception.
Please help me with my mistake.
Below is the implementation of LinkList where all the methods are defined
class LinkedListNode {
public LinkedListNode next;
public LinkedListNode prev;
public LinkedListNode last;
public int data;
public LinkedListNode(int d, LinkedListNode n, LinkedListNode p) {
data = d;
setNext(n);
setPrevious(p);
}
public void setNext(LinkedListNode n) {
next = n;
if (this == last) {
last = n;
}
if (n != null && n.prev != this) {
n.setPrevious(this);
}
}
public void setPrevious(LinkedListNode p) {
prev = p;
if (p != null && p.next != this) {
p.setNext(this);
}
}
public String printForward() {
if (next != null) {
return data + "->" + next.printForward();
} else {
return ((Integer) data).toString();
}
}
public LinkedListNode clone() {
LinkedListNode next2 = null;
if (next != null) {
next2 = next.clone();
}
LinkedListNode head2 = new LinkedListNode(data, next2, null);
return head2;
}
}
You are getting an exception just because of the following condition:
while(curr != null)
Replace it with while(curr != null && curr.next != null) this way you can check if you have the next element.
Hope this helps.
The problem is that here:
while(curr != null)
{
if(curr.next.data==current.data) //Getting error at this line
curr.next = curr.next.next;
else
curr = curr.next;
}
You are accessing the curr.next.data where you are not checking if that node is null or not. This through your NullPointerException.
To fix your problem is to check on the while loop, if the .next is also not null.
while(curr != null && curr.next != null)
{
if(curr.next.data==current.data) //Getting error at this line
curr.next = curr.next.next;
else
curr = curr.next;
}
In other words, you are not checking if your next node is actually the end of the linked list (i.e null). If you need in your program logic to handle this separately, then you should remove the check from the while loop, and implement this check differently.
I'm attempting to write a class to create a prefix tree (or trie) with an addWord method that takes in a string as a parameter and stores each character in it's appropriate place in the tree.
However, I keep getting a NullPointerException in the line of my first if statement (indicated below). Can anyone help me understand what's causing this? Thank you in advance!
public class PrefixTree {
private Node root;
public PrefixTree () {
root = new Node();
}
public void addWord(String word) {
int length = word.length();
char currentCharacter = word.charAt(0);
Node currentNode = root;
//Essentially this is saying "for each character in the string..."
for(int i=0; i<length; i++){
currentCharacter= word.charAt(i);
//if the children array of parent node does not contain the current character
//create a new node and add it to the parent array.
//HERE IS WHERE THE EXCEPTION IS BEING THROWN
if(currentNode.children[currentCharacter - 'a'] == null) {
Node newNode = new Node();
//set the node character value equal to the current character
newNode.c=currentCharacter;
//add the new node to the child array of its parent node
currentNode.children[currentCharacter - 'a']= newNode;
//if this is the last character in the word, change the endWord value to true
if( i == length-1) {
newNode.endWord = true;
//stores the complete string in its ending node
newNode.fullWord = word;
}
//set current node equal to the new node created and repeat the process
currentNode = newNode;
}
}
}
private class Node {
public boolean endWord;
public char c;
public Node[] children;
public String fullWord;
public Node(){
c = '0';
endWord = false;
Node[] children = new Node[26];
//Stores the complete string of a word ending w/ this node to make life easier later
String fullWord = null;
}
}
public static void main(String [] args){
PrefixTree test = new PrefixTree();
test.addWord("test");
}
}
Because you're assigning to local variables in Node's constructor. Change to this:
public Node(){
c = '0';
endWord = false;
this.children = new Node[26];
//Stores the complete string of a word ending w/ this node to make life easier later
this.fullWord = null;
}
import java.util.*;
public class MyTwoWayLinkedList<E> extends java.util.AbstractSequentialList<E> {
private Node<E> head, tail;
private int size = 0;
private List<E> list;
/** Create a default list */
public MyTwoWayLinkedList() {
list = new LinkedList<E>();
}
public MyTwoWayLinkedList(E[] objects) {
list = new LinkedList<E>();
for (int i = 0; i < objects.length; i++)
add(objects[i]);
}
/** Return the head element in the list */
public E getFirst() {
if (size == 0) {
return null;
}
else {
return head.element;
}
}
/** Return the last element in the list */
public E getLast() {
if (size == 0) {
return null;
}
else {
return tail.element;
}
}
/** Add an element to the beginning of the list */
public void addFirst(E e) {
Node<E> newNode = new Node<E>(e); // Create a new node
newNode.next = head; // link the new node with the head
head.previous = newNode; //link the old node with new head
head = newNode; // head points to the new node
size++; // Increase list size
if (tail == null) // the new node is the only node in list
tail = head;
}
/** Add an element to the end of the list */
public void addLast(E e) {
Node<E> newNode = new Node<E>(e); // Create a new for element e
if (tail == null) {
head = tail = newNode; // The new node is the only node in list
}
else {
tail.next = newNode;// Link the new with the last node
newNode.previous = tail;
tail = tail.next; // tail now points to the last node
}
size++; // Increase size
}
#Override /** Add a new element at the specified index
* in this list. The index of the head element is 0 */
public void add(int index, E e) {
if (index == 0) {
addFirst(e);
}
else if (index >= size) {
addLast(e);
}
else {
Node<E> current = tail;
for (int i = size - 1; i > index; i--) {
current = current.previous;
}
Node<E> temp = current.next;
current.next = new Node<E>(e);
(current.next).previous = current;
(current.next).next = temp;
size++;
}
}
/** Remove the head node and
* return the object that is contained in the removed node. */
public E removeFirst() {
if (size == 0) {
return null;
}
else {
Node<E> temp = head;
head = head.next;
head.previous = null;
size--;
if (head == null) {
tail = null;
}
return temp.element;
}
}
/** Remove the last node and
* return the object that is contained in the removed node. */
public E removeLast() {
if (size == 0) {
return null;
}
else if (size == 1) {
Node<E> temp = head;
head = tail = null;
size = 0;
return temp.element;
}
else {
Node<E> temp = tail;
tail = tail.previous;
tail.next = null;
size--;
return temp.element;
}
}
#Override /** Remove the element at the specified position in this
* list. Return the element that was removed from the list. */
public E remove(int index) {
if (index < 0 || index >= size) {
return null;
}
else if (index == 0) {
return removeFirst();
}
else if (index == size - 1) {
return removeLast();
}
else {
Node<E> previous = tail;
for (int i = size - 1; i > index; i--) {
previous = previous.previous;
}
Node<E> current = previous.next;
(current.next).previous = previous;
previous.next = current.next;
size--;
return current.element;
}
}
#Override /** Override toString() to return elements in the list */
public String toString() {
StringBuilder result = new StringBuilder("[");
Node<E> current = tail;
for (int i = size - 1; i > 0; i--) {
result.append(current.element);
current = current.previous;
if (current != null) {
result.append(" ,"); // Separate two elements with a comma
}
else {
result.append("["); // Insert the closing ] in the string
}
}
return result.toString();
}
#Override /** Clear the list */
public void clear() {
size = 0;
head = tail = null;
}
#Override /** Override iterator() defined in Iterable */
public ListIterator<E> listIterator() {
Node<E> current = head; // Current index
return list.listIterator();
}
#Override /** Override iterator() defined in Iterable */
public ListIterator<E> listIterator(int index) {
Node<E> current = head; // Current index
for (int i = 0; i < index; i++) { // sets current int to the parameter
current = current.next;
}
return list.listIterator();
}
#Override
public int size()
{
return size;
}
public class Node<E> {
E element;
Node<E> next;
Node<E> previous;
public Node(E element) {
this.element = element;
}
}
}
This is my original class, I will include my test case below but first let me explain my problem. I am trying to create a Doubly linked list and iterate backwards through it. However I am getting a Null Pointer Exception by just adding elements to the list. I have looked over the section of code for my addFirst method for about 2 hours now and don't see any logic errors(doesn't mean there arent any), please help!
Here is my test case as promised.
public class TestMyLinkedList {
/** Main method */
public static void main(String[] args) {
// Create a list for strings
MyTwoWayLinkedList<String> list = new MyTwoWayLinkedList<String>();
// Add elements to the list
list.add("America"); // Add it to the list
System.out.println("(1) " + list);
list.add(0, "Canada"); // Add it to the beginning of the list
System.out.println("(2) " + list);
list.add("Russia"); // Add it to the end of the list
System.out.println("(3) " + list);
list.addLast("France"); // Add it to the end of the list
System.out.println("(4) " + list);
list.add(2, "Germany"); // Add it to the list at index 2
System.out.println("(5) " + list);
list.add(5, "Norway"); // Add it to the list at index 5
System.out.println("(6) " + list);
list.add(0, "Poland"); // Same as list.addFirst("Poland")
System.out.println("(7) " + list);
// Remove elements from the list
list.remove(0); // Same as list.remove("Australia") in this case
System.out.println("(8) " + list);
list.remove(2); // Remove the element at index 2
System.out.println("(9) " + list);
list.remove(list.size() - 1); // Remove the last element
System.out.print("(10) " + list + "\n(11) ");
for (String s: list)
System.out.print(s.toUpperCase() + " ");
list.clear();
System.out.println("\nAfter clearing the list, the list size is "
+ list.size());
}
}
I'm not completely sure why you are using a LinkedList within your own implementation of a Double Linked List. In regards to your question about your addFirst method however, I have the following comments and an example of how I would approach this solution.
Head is null when you call the addFirst method.
Head has not been initialized as a new Node.
Therefore newNode.next = head; is actually newNode.next = null; There is your null pointer exception, I would imagine!
public void addFirst (E e)
{
Node<E> newNode = new Node<E>(e); //create new node
if (head != null){ //if head exists
newNode.next = head; //the new node's next link becomes the old head
}
head = newNode; //the new head is the new node
if (tail == null){ //if the tail is non existent ie head the only object in list
tail = head; //the head and the tail are the same
head.next = tail; //the 'next' value of head will be tail
}
head.prev = tail; //the previous node to head will always be tail
size++;
}
}