For my last assignment, I made an Inventory program, using Arrays. Our final assignment is to change the Array to a Linked List. We are not to use the LinkedList class, we are to create our own. I got my program working, but my instructor said it is only okay, but could be better. Mainly, my findItem method, in my InventoryLL class. My question is: is there a better way to go about finding an Item in my Linked List? Any suggestions would be greatly appreciated, I have gotten 100% on each assignment so far, just trying to finishing strong, and learn as much as I can :)
public ItemNode findItem()
{
boolean found = false;
int inputID = 0;
ItemNode current = head;
try{
System.out.print("\nGreetings, please enter the ID number for item:\n");
inputID = scannerObject.nextInt();
scannerObject.nextLine();
while (found != true){
if (current.getID() == inputID){
found = true;
break;
}
current = current.getNext();
}
}catch(Exception e)
{
System.out.println("\nERROR!");
}
return current;
}
The short answer, is that you can't make it more efficient without making it into a (for example) skip list, which is an ordered linked list, that includes a sort of "express path".
Wikipedia has a well written article that explains both the implementation of the list, as well as the searching of it
Though it might be a little bit out of scope.
Well, in your code you're assuming that 'found' will eventually come true; you should be aware that it could not happen. Also, you can change the loop for avoiding using a "break", which is not very smart, altough it is not wrong.
You could too pass the value of inputID through the parameters, so your call to the function will be findItem(0) (or findItem(7) or whatever you like)
public ItemNode findItem(inputID){
boolean found = false;
for (itemNode current = head; !found; current = current.getNext()){
if (current.getID() == inputID){
found = true;
}
}
if (found) {
return current;
}
else{
System.out.println("not found"); //or some other code
}
Related
I'm currently programming on a little project (which is way to specific to explain here) and I got everything working except one part. I've got a List pZiegel by parameter which is modified in recursion. Because it didn't work, I did a little debugging and found the problem: At one point, the list contains exactly one number at the end of the method. Then, the program jumps one recursion depth back. And directly after that, it doesn't contains any numbers anymore. How did it lose the number? Lists as parameters work with pass-by-reference, so it shouldn't just reject it, right?
public void erstelleBaum (Tree pTree, List<Integer> pZiegel, List<Integer> pFugen, int tiefe) {
if (tiefe / n >= maxHoehe) {
System.out.println("hi");
mauerGefunden = true;
alleFugen = pFugen;
}
if (!mauerGefunden) {
pZiegel.toFirst();
while (pZiegel.hasAccess() && !mauerGefunden) {
boolean ziegelHinzufügen = false;
möglich = true;
aktZiegel = pZiegel.getContent();
// ...
if (möglich) {
// ...
pZiegel.remove();
if (pZiegel.isEmpty()) {
ziegelHinzufügen = true;
pZiegel = new List();
for (int i = 1; i <= n; i++) {
pZiegel.append(i);
}
}
// Recursion
erstelleBaum(neuesBlatt, pZiegel, neueFugen, neueTiefe);
// Here, it tells me that pZiegel is empty (at recursion depth 17)
if (ziegelHinzufügen) {
pZiegel.toFirst();
while (pZiegel.hasAccess()) {
pZiegel.remove();
}
pZiegel.append(aktZiegel);
}
else {
pZiegel.toFirst();
while (pZiegel.hasAccess() && pZiegel.getContent() < aktZiegel) {
pZiegel.next();
}
if (pZiegel.hasAccess()) {
pZiegel.insert(aktZiegel);
pZiegel.toFirst();
while (pZiegel.getContent() != aktZiegel) {
pZiegel.next();
}
}
else {
pZiegel.toLast();
pZiegel.append(aktZiegel);
pZiegel.toLast();
}
}
}
pZiegel.next();
}
}
// Here, pZiegel contained one number (at recursion depth 18)
}
I hope, the code isn't too messy. I tried to keep out the parts that doesn't involve pZiegel. And sorry, that the variables are named in german. I didn't want to change them for this post because I know I would forget to change something in the code.
Feel free to ask, if something is unclear.
I believe the pZiegel List reference is being lost at some point. You should check the pZiegel object ID (a number displayed when you inspect the object) to make sure it is the same List instance all over the recursions.
Notice that there's one part of your code that makes the pZiegel identifier reference a new List:
...
if (pZiegel.isEmpty()) {
ziegelHinzufügen = true;
pZiegel = new List(); // <---- this line
for (int i = 1; i <= n; i++) {
pZiegel.append(i);
}
}
...
I believe you are calling the 18th recursion with pZiegel referencing one list (maybe empty). Inside the 18th recursion that line is called and pZiegel starts referencing a new List (realize that the last List still exists and is referenceed by the pZiegiel identifier of the 17th recursion). On the last line of the 18th recursion call you believe you are inspecting the same pZiegiel List from the 17th recursion, but that's not the case.
I'm trying to do a linkedlist for an assigment i have, this ask explicitly to create, from scratch a linkedlist and some derivated types like a queue and a stack, this is just some college homework, and i realize how to make a node class and a linkedlist class, but i'm struggling to create the addAll() method in this linkedlist class, this is what i have.
if i must bet, i say is the Collection c one, but then, i'm trying to add list of stuff there, in order to pass him's content to the new list, obiusly is not ready and obiusly doesn't work.
Can you tell me how i can pass some kind of "proto-list" in order to pass them data inside the new list?
(I know i must use somekind of for(objects) but i'm failing to pass some data through the parameter, which will be the right parameter to put there?)
public boolean addAll(Collection c) {
for (int i = 0; i < (this.listaNodos.size()); i++) {
//for (T someT : c){
// Node newNodo = new Node(someT);
//}
//i know the one down there is not gonna do anything, because
//i'm not accesing the data, but one problem at a time would ya ;)
Node newNodo = new Node(someT);
Node actualNodo = this;
boolean processFinished = false;
try{
if(index >= this.listaNodos.size() || index < 0){
throw new IndexOutOfBoundsException();
}
do{
if(index == actualNodo.getIndex())
{
actualNodo.setData(someT);
processFinished = true;
return true;
}
else
{
actualNodo = actualNodo.nextNode;
}
}while(!processFinished);
return false;
}catch(IndexOutOfBoundsException ex)
{
throw ex;
}
}
return false;
}
Can you tell me how to fix it to make it work?
Any request for clarification, constructive comment, or question would be greatly apreciated too.
Thanks in advance
I assume you already have an add() method of some sort right? If so, you can go over each element in c and add it using the add method:
public boolean addAll(Collection<T> c) {
boolean changed = false;
for (T t:c) {
changed |= this.add(t);
}
return changed;
}
I'm assuming the returned boolean means whether this list has changed, this is how it is defined in the Collection contract: https://docs.oracle.com/javase/7/docs/api/java/util/Collection.html#addAll(java.util.Collection).
You were also missing a generic type for your add method, so I added one. I assume your class definition looks somthing like this?
public class MyLinkedList<T>
I am working on a robot maze where the robot finds the target without bumping into walls. As a "backtrack" method, I need the robot to go in the opposite direction as it did when it first came across a junction. This is my code:
This should work. I think you may have forgot to continue iterating through the list after you did the initial Junction currentJunction = junctionIterator.next();, so you never really moved through the list. Also, you may want to always check hasNext() before using next() in case there is an empty list.
public int searchJunction(IRobot robot) {
boolean foundJunction = false;
Junction currentJunction = null;
//Iterate through list until the end, or until correct junction is found.
while (!foundJunction && junctionIterator.hasNext()) {
currentJunction = junctionIterator.next();
if ((((currentJunction.x)==(robot.getLocation().x))) && ((currentJunction.y)==(robot.getLocation().y))) {
foundJunction = true;
}
}
return currentJunction;
}
Hope this clears things up.
inside the while loop you're having trouble with you don't seem to be going through to the last junction... Is this by design? Or should it be
while (junctionIterator.hasNext()) {
if ((((currentJunction.x)==(robot.getLocation().x))) && ((currentJunction.y)==(robot.getLocation().y)))
break;
currentJunction = junctionIterator.next();
}
Let me know if this helps or if I misunderstood what you're asking
Please find below my implementation for DFS.
protected void DFS(String search) {
for(Tree<T> child : leafs) {
if(child.value.equals(search))
return;
else
child.DFS(search);
System.out.println(child.value);
}
}
The objective is to stop traversal on finding the node whose value is in the variable search. However, the above function goes on traversing the tree even beyond the declared search node. Could someone help me modify the above function?
Thank you.
Edit 1
protected boolean DFS(String anaphorKey) {
boolean found = false;
for(Tree<T> child : leafs) {
if(child.head.equals(anaphorKey))
return true;
found = child.DFS(anaphorKey);
if(found == true)
break;
System.out.println(child.head);
//System.out.println("anaphorKey: "+anaphorKey);
}
return found;
}
Tried implementing the given answer suggestion (#SJuan76). The implementation above isn't working as desired. Could you point me to the place where code is not as per the logic suggested?
rookie, might I suggest an implementation using the classic for-loop (as opposed to the enhanced for-loop being used now) which allows integration of your stop-condition a bit better, something like:
protected boolean DFS(String key) {
boolean found = false;
for(int i = 0; i < leafs.size() && !found; i++) {
Tree<T> child = leafs.get(i);
if(child.head.equals(key))
found = true;
else
found = child.DFS(key);
}
return found;
}
So as soon as your found condition is hit, the 'found' becomes true and your loop stops.
What you may have forgotten is the "found = child.DFS(key)" portion of the recursion, where you need to remember the result of your recursive calls so ALL your for-loops on up the chain all break as soon as you return.
Hope that helps.
Option A (Nice): the function returns a value, when the node is found it returns a different value that if the node was not found. When you call to method, if you get the found value you stop the loop and return the found value too.
Option B (Ugly): When found, thow an Exception (better if it is your own implementation of it). Don't forget to catch it.
Option C (Uglier): The same with global (static) variables.
UPDATE 1:
It looks like your method should run ok now, can you check (System.out.println) if your value is ever found?
In a more personal opinion, I would find
protected boolean DFS(String anaphorKey) {
for(Tree<T> child : leafs) {
if(child.head.equals(anaphorKey))
return true;
if(child.DFS(anaphorKey)) // No need to store value. No need to check == true (it is implicit)
return true; // If we are in this line the value was found, always return true
System.out.println(child.head);
//System.out.println("anaphorKey: "+anaphorKey);
}
return false; // If the method did not exit previously it was because the value was not found, so in this line always return false
}
more readable (but it should work exactly as your implementation)
This is for homework but please know that I have looked online for help (such as http://www.sethi.org/classes/class_stuff/cis435/others/notes-java/data/collections/lists/simple-linked-list.html) and my textbook but I am still having some issues.
Any help would be appreciated...
Right now I'm trying to just insert values in but nothing is working. Whether it's the first item, whether it's being added as the last one, or somewhere in between.
Node header = null; // First element of list.
Node back = null; // Last element of list.
public void insert(int i, double value){ //insert value before i-th element
Node e = new Node();
e.num = value;
Node curr = header;
for(int x=0;x<i;x++) {
if (i == 1) { //we want to insert as first thing
if (size == 0) { //its the FIRST time we add something
header.next = e;
e.next = back;
break;
} else if (size == 1){
e.next = header.next; //i.e. the second thing in the list
header.next = e;
break;
} else {
e.next = header.next.next; //i.e. the second thing in the list
header.next = e;
break;
}
}
else if (x == (i-1)) {
e.next = curr.next;
curr.next = e;
break;
}
curr = curr.next;
}
size = size+1;
}
Not really sure why it isn't working.
Thanks!
For some reason, people who are still learning to program make things far more complicated then they need to be. I did it when I was learning java, I still do it when I am just getting into a new language, and students that I have marked find new and amazing ways to do it. You have more going on in your insert then there needs to be, for example, a method that inserts a value at a specific index should not check if it's the first item to be inserted (not saying it shouldn't check bounds). Here is the pseudo code of what I would do.
insert(index, value)
if index>size
throw null pointer
traverse to index -1 //lets call this nodeI
create newnode and set value
set newnode.next to nodeI.next
set nodeI.next to newnode
increase size.
Couple of handy hints for you, you should have a function to get an element from the link list, something that returns a node? public node elementAt(int index) for example? use that to traverse the linked list. If you want to append to the Linked list, try this
append(value)
insert(size-1,value)
and if you want to insert at the beginning? same idea
insert(value)
insert(0,value)
In the line e.next = header.next.next what would happen if header.next points to a 'null'? Is it possible to get there?
What are the corner cases you have to deal with and have you taken them all into account?
Can you start with the simplest case first, adding either an element to the front or an element to the back? Then use those functions to implement the insert?
A few suggestions:
implement java.util.List
Think about generics
Read this.
Start with "insert at the end" before you think about "insert at i".
I have tried a simple program, which will be useful for you guys, I am also learning Java, please bear with me for any mistakes, but this program works fine.
I am posting a very simple singly linked list program in Java, which I tried out today.
I hope it will help all.
LinkList.java
class LinkList
{
public static void main(String args[])
{
Node node = new Node(1);
node.addAtLast(2);
node.addAtLast(3);
node.addAtLast(4);
node.addAtLast(5);
node.printList();
}
}
Node.java
class Node
{
private int data;
private Node link;
public Node(int mydata)
{
data = mydata;
link = null;
}
public void printList()
{
System.out.print("|"+data+"|"+"->");
if(link != null)
{
//recursive call
link.printList();
}
else
{
//marking end of list as NULL
System.out.print("|NULL|");
}
}
public void addAtLast(int mydata)
{
if(link == null)
{
link = new Node(mydata);
}
else
{
link.addAtLast(mydata);
}
}
}
OUTPUT :
The below is our output
|1|->|2|->|3|->|4|->|5|->|NULL|