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Couldn't implement binary search on linked list

i am a cse student who takes data structures course. Trying to implement binary search algorithm to my SinglyLinkedList class, somehow i've failed. Could you check it what's wrong please ?
The related method;
I've debugged and it just enters the loops this side: else if(temp.getElement() > target)
public int binarySearchLinkedList(SinglyLinkedList<E> list, E target) {
int left = 0;
int right = list.getSize();
while (left <= right) {
int mid = (left + right) / 2;
Node<E> temp = head;
for (int i = 0; i < mid - 1; i++) {
temp = temp.next;
}
if (temp.getElement() instanceof Number && target instanceof Number) {
if (Integer.parseInt(temp.getElement().toString()) == Integer.parseInt(target.toString())) {
return mid;
} else if (Integer.parseInt(temp.getElement().toString()) > Integer.parseInt(target.toString())) {
left = mid + 1;
} else {
right = mid - 1;
}
}
}
All class for better understanding;
public class SinglyLinkedList<E> {
private static class Node<E> {
private E element;
private Node<E> next;
public Node(E e, Node<E> n) {
element = e;
next = n;
}
private E getElement() {
return element;
}
private Node<E> getNext() {
return next;
}
private void setNext(Node<E> n) {
next = n;
}
}
private Node<E> head;
private Node<E> tail;
private int size;
public SinglyLinkedList() {
};
public int getSize() {
return size;
}
public void append(E e) {
if (head == null) {
head = new Node<E>(e, null);
tail = head;
size++;
return;
}
Node<E> temp = head;
while (temp != tail) {
temp = temp.next;
}
temp.setNext(tail = new Node<E>(e, null));
size++;
return;
}
public int binarySearchLinkedList(SinglyLinkedList<E> list, E target) {
int left = 0;
int right = list.getSize();
while (left <= right) {
int mid = (left + right) / 2;
Node<E> temp = head;
for (int i = 0; i < mid - 1; i++) {
temp = temp.next;
}
if (temp.getElement() instanceof Number && target instanceof Number) {
if (Integer.parseInt(temp.getElement().toString()) == Integer.parseInt(target.toString())) {
return mid;
} else if (Integer.parseInt(temp.getElement().toString()) > Integer.parseInt(target.toString())) {
left = mid + 1;
} else {
right = mid - 1;
}
}
}
return -1;
}
public String toString() {
StringBuilder sb = new StringBuilder();
Node<E> temp = head;
while (temp != tail) {
sb.append(temp.getElement()).append(", ");
temp = temp.next;
if (temp == tail) {
sb.append(temp.getElement());
}
}
return sb.toString();
}
}
And the main method;
public static void main(String[] args) {
SinglyLinkedList<Integer> list = new SinglyLinkedList<>();
list.append(10);
list.append(20);
list.append(30);
list.append(40);
list.append(50);
list.append(60);
list.append(70);
list.append(80);
list.append(90);
list.append(100);
System.out.println(list);
System.out.println(list.binarySearchLinkedList(list, 30));
}
It returns;
10, 20, 30, 40, 50, 60, 70, 80, 90, 100
-1

I'm guessing this line is the biggest issue:
for (int i = 0; i < mid - 1; i++) {
Consider what happens if mid is 1. The loop won't execute, because it is not the case that 0 < 1-1. So the inspected node won't be the one you think it is. The actual node at index mid will never be inspected. So the outer loop will eventually exit, never having found the target. Presumably your method ends with return -1;.
Other issues include:
You're initializing right to an exclusive value, but treat it as inclusive elsewhere. Consider using int right = list.getSize() - 1;
You've declared a generic method, but implemented it only for Integer. One way around this would be to limit the generic type to one that supports Comparable - e.g., E extends Comparable<E>.
You're implementing a binary search in a linked list. In a linked list, linear search would be simpler and no less efficient. Or you could use a data structure that supports constant-time access by index, such as an array or ArrayList.

LinkedList (built from scratch) add() not working

I'm working on a class assignment where I must build a singly linkedlist class from scratch. My problem here is that my add() method isn't quite working when I iterate through a series of items and add them to a linkedlist. More specifically, 1) it is duplicating the first one in a series, and 2) it is not adding the last one in a series. What is wrong with my add() method in the ManualLinkedList class?
public class test {
static class ManualLinkedList<T> {
private static class Node<T> {
T item;
Node<T> next;
Node<T> prev;
public T getItem() {
return item;
}
public ManualLinkedList.Node<T> getNext() {
return next;
}
Node(Node<T> prev, T element, Node<T> next) {
this.item = element;
this.next = next;
this.prev = prev;
}
}
Node<T> head;
Node<T> tail;
int size = 0;
public void add(T t) {
final Node<T> l = tail;
final Node<T> newNode = new Node<>(l, t, null);
tail = newNode;
if (l == null) {
head = newNode;
}
else {
l.next = newNode;
}
size++;
}
public int size() { return size; }
public T getContentFromPosition(int position) {
Node<T> np = head;
T result = head.getItem();
if (position == size) {
result = tail.getItem();
}
for (int i = 1; i < size; i++) {
if (i == position) {
result = np.getItem();
}
np = np.getNext();
}
return result;
}
} //end ManualLinkedList class
public static void main(String[] args) {
ManualLinkedList<Integer> test = new ManualLinkedList<>();
test.add(1);
test.add(2);
test.add(3);
test.add(4);
test.add(5);
test.add(6);
test.add(7);
test.add(8);
for (int i =0; i < test.size; i++){
System.out.println(test.getContentFromPosition(i));
}
}
}
Expected Output:
1
2
3
4
5
6
7
8
Actual Output:
1
1 // notice the duplicate first item
2
3
4
5
6
7 // notice the missing 8, or the last input

Primary Issues
index is used as 0..size-1 during invocation
for loop in getContentFromPosition should be from 0..size-1
The usage of size == position is irrelevant in getContentFromPosition
Code
public T getContentFromPosition(int position) {
if (position >= size) {
return null;
}
Node<T> np = head;
T result = head.getItem();
if (position == size - 1) {
result = tail.getItem();
}
for (int i = 0; i < size; i++) {
if (i == position) {
result = np.getItem();
break;
}
np = np.next;
}
return result;
}
} //end ManualLinkedList class
public static void main(String[] args) {
ManualLinkedList<Integer> test = new ManualLinkedList<>();
test.add(1);
test.add(2);
test.add(3);
test.add(4);
test.add(5);
test.add(6);
test.add(7);
test.add(8);
for (int i = 0; i < test.size; i++){
System.out.println(test.getContentFromPosition(i));
}
}

Your add function is actually fine.
However, your getContentFromPosition function is almost right, but needs a little work. You should decide whether the positions in your list count from 0 or from 1. For example, if there are 3 elements in a list, are they are positions 0, 1, 2 or positions 1, 2, 3?
When you are using the getContentFromPosition function from main, you are assuming that positions count from 0, but in writing the function, it looks like you were assuming that they count from 1.
If you modify the getContentFromPosition to count from 0, then you can get rid of the special case checking for position==size, and you would then start the loop at 0, not 1. Also, for efficiency, why not return the result when you find it rather than let the loop continue to run?

you need to initialized int size=1 instead of 0
and in the main method for loop change to int i=1 instead of 0

in getContentFromPosition method, your for loop should start from 0. Rest is fine.
for (int i = 0; i < size; i++)

Swapping nodes in a singly linked list java

I have been trying to come up with an algorithm to swap 2 nodes (not necesarily right next to each other) in a singly linked list for 2 days but for some reason I cannot do it.
Here is what I have, I am really new to coding and have been really stressed:
I have managed to place a temp node in but can't actually swap the nodes.
public void swap(int i, int j) {
current = head;
current2 = head;
sllNode temp = new sllNode(" ");
sllNode temp2 = new sllNode(" ");
for(int z = 0; i>z; z++)
current=current.next;
for(int q = 0; j>q; q++)
current2 = current2.next;
temp.next = current2.next.next;
current.next = temp;
current.next = current2.next.next;
current2.next = current;

Why exchange nodes, when you can exchange the data?
public void swap(int i, int j) {
sllNode ithNode = head;
for (int z = 0; z < i; z++) {
ithNode = ithNode.next;
}
sllNode jthNode = head;
for (int q = 0; q < j; q++) {
jthNode = jthNode.next;
}
// Swap the data
String data = ithNode.data;
ithNode.data = jthNode.data;
jthNode.data = data;
}
It would make sense to use a method:
public sllNode get(int i) {
sllNode current = head;
while (i > 0) {
current = current.next;
}
return current;
}
By the way:
The convention for class names is a beginning capital: SllNode.
Do not use fields for things like current and current2 where they can be local variables.
Exchanging nodes, the hard way
Here one has to think, so it is best to deal with special cases first, and then only treat i < j.
public void swap(int i, int j) {
if (i >= size() || j >= size()) {
throw new IndexOutOfBoundsException();
}
if (i == j) {
return;
}
if (j < i) {
swap(j, i);
return;
}
// i < j
sllNode ithPredecessor = null;
sllNode ithNode = head;
for (int z = 0; z < i; z++) {
ithPredecessor = ithNode;
ithNode = ithNode.next;
}
sllNode jthPredecessor = ithNode;
sllNode jthNode = ithNode.next;
for (int q = i + 1; q < j; q++) {
jthPredecessor = jthNode;
jthNode = jthNode.next;
}
// Relink both nodes in the list:
// - The jthNode:
if (ithPredecessor == null) {
head = jthNode;
} else {
ithPredecessor.next = jthNode;
}
sllNode jNext = jthNode.next;
//if (ithNode.next == jthNode) {
if (jthPredecessor == ithNode) {
jthNode.next = ithNode;
} else {
jthNode.next = ithNode.next;
}
// - The ithNode:
if (jthPredecessor == ithNode) {
} else {
jthPredecessor.next = ithNode;
}
ithNode.next = jNext;
}
No guarantee that the logic is okay. There are tricks:
//if (ithNode.next == jthNode) {
if (jthPredecessor == ithNode) {
Both conditions test whether i + 1 == j, but testing on a .next and then assigning makes the condition a momentary state. As you see it would have been easier to have one single if (i + 1 == j) { ... } else { ... } and handle both the ithNode and jthNode.

To do this, you need to swap 2 things: the node as next from the previous node, and the next node.
Once you found current and current2 which are the previous nodes of the nodes you want to swap, do this:
Swap the nodes:
sllNode tmp = current.next;
current.next = current2.next;
current2.next = tmp;
Then swap the next:
tmp = current.next.next;
current.next.next = current2.next.next;
current2.next.next = tmp;

// Swapping two elements in a Linked List using Java
import java.util.*;
class SwappingTwoElements {
public static void main(String[] args)
{
LinkedList<Integer> ll = new LinkedList<>();
// Adding elements to Linked List
ll.add(10);
ll.add(11);
ll.add(12);
ll.add(13);
ll.add(14);
ll.add(15);
// Elements to swap
int element1 = 11;
int element2 = 14;
System.out.println("Linked List Before Swapping :-");
for (int i : ll) {
System.out.print(i + " ");
}
// Swapping the elements
swap(ll, element1, element2);
System.out.println();
System.out.println();
System.out.println("Linked List After Swapping :-");
for (int i : ll) {
System.out.print(i + " ");
}
}
// Swap Function
public static void swap(LinkedList<Integer> list,
int ele1, int ele2)
{
// Getting the positions of the elements
int index1 = list.indexOf(ele1);
int index2 = list.indexOf(ele2);
// Returning if the element is not present in the
// LinkedList
if (index1 == -1 || index2 == -1) {
return;
}
// Swapping the elements
list.set(index1, ele2);
list.set(index2, ele1);
}
}
Output
Before Swapping Linked List :-
10 11 12 13 14 15
After Swapping Linked List :-
10 14 12 13 11 15
Time Complexity: O(N), where N is the Linked List length

trying to implement quick sort and use insertion sort when the listsize is <= 10. getting incorrect returns

import java.util.Comparator;
public class SortedList implements Container{
private int size;
private int front = 0;
private int rear = 0;
private WorkOrder[] buffer;
Comparator comparator;
public SortedList(){
buffer = new WorkOrder[10];
}
/**
* The comparator that the container will use to arrange the container
*
* #param comp
*/
public void setComparator(Comparator comp){
if (comp == null){
throw new IllegalArgumentException();
}
comparator = comp;
}
/**
* Add a workorder to the container
*/
public void add(WorkOrder wo){
if(wo == null){
throw new IllegalArgumentException();
}
if (size == capacity()){
WorkOrder[] regrowArray = new WorkOrder[2*capacity()];
for (int i = 0; i<size;i++){
regrowArray[i] = buffer[i];
}
buffer = regrowArray;
rear = size;
}
buffer[rear] = wo;
rear++;
size++;
}
/**
* Gets a workorder (removes it also) from the container
*/
public WorkOrder getNext(){
if (isEmpty()){
return null;
}
WorkOrder itemRemoved = buffer[front];
buffer[front] = null;
front++;
size--;
return itemRemoved;
}
/**
* Arranges the workorders in the required order
* Uses the comparator if necessary
* Some data structures may not need this method (like Queue)
* Just make it a no-op for those structures.
*/
public void arrange(){
if (buffer == null || size == 0){
return;
}
partition(0,size-1);
//sort(0,size-1);
}
private void partition(int left, int right){
int pivotIndex = (right + left) / 2;
int i = left;
int j = right;
if ((right-left) <= 10){
insertionSort(left,right);
return;
}
while (i <= j){
while (comparator.compare(buffer[i],buffer[pivotIndex]) < 0){
i++;
}
while (comparator.compare(buffer[j],buffer[pivotIndex]) > 0){
j--;
}
if (i <= j){
swap(i,j);
i++;
j--;
}
}
if (left < j){
partition(left,j);
}
if (i<right){
partition(i, right);
}
}
private void insertionSort(int left, int right){
for (int i = 1; i < right; i++){
WorkOrder val = buffer[i];
int j = i - 1;
while (j>=0 && comparator.compare(buffer[j], val) > 0){
buffer[j+1] = buffer[j];
j = j - 1;
}
buffer[j+1] = val;
}
}
private void swap(int x, int y){
WorkOrder temp = buffer[x];
buffer[x] = buffer[y];
buffer[y] = temp;
}
}
the output I see is:
0123567894
The comparator being passed in is dependent on the junits being run on it so that is why I am using comparator. compare for everything. I'm almost positive the sorting algos are correct, I could be manipulating the backing array incorrectly.

The problem seems its the insertion sort part:
for (int i = 1; i < right; i++){ //going from 1 to one previous to the last (right - 1)
WorkOrder val = buffer[i];
int j = i - 1;
while (j>=0 && comparator.compare(buffer[j], val) > 0){
buffer[j+1] = buffer[j];
j = j - 1;
}
buffer[j+1] = val;
}
you need to take into account that it needs to loop until the last one, since you know that the right variable is the last index of that partition.
for (int i = 1; i <= right; i++) //replace < for <=
since right is the last index (and it needs to be taken into account) of the array when its 10 or less elements.
edit:
The only thing else i see (in the quick sort code) is this part:
if (left < j){
partition(left,j); //trying to partition from left to j (since 'j' and 'i' may overlap)
}
it should be
if (left < (i - 1)){
partition(left,i - 1); //so the partition doesnt overlap with the 'i' to 'right' partition by an element (since i and j may overlap at the end).
}
That way you ensure that you are splitting the partition in half at all times.

Recursive function in java - N nested loops with changing indicies

Similar to this: Is there any way to do n-level nested loops in Java?
I want to create a recursive function, which generates N nested loops, where the indicies depend on the depth of the loop. So basically, I want to do this recursively:
// N = 3, so we want three nested loops
for(int i1 = 0; i1 < max; i1++){
for(int i2 = i1+1; i2 < max; i2++){
for(int i3 = i2+1; i3 < max; i3++){
int value1 = getValue(i1);
int value2 = getValue(i2);
int value3 = getValue(i3);
doSomethingWithTheValues( ... );
}
}
}
I've looked at the answers in the other question, and tried to modify the answer (by oel.neely), but without luck. My guess is that it only needs a small modification, but right now, I'm just confusing myself!

Its C#, but should be easily convertable to Java:
class ImmutableStack<T>
{
public readonly T Head;
public readonly ImmutableStack<T> Tail;
public ImmutableStack(T head, ImmutableStack<T> tail)
{
this.Head = head;
this.Tail = tail;
}
public static ImmutableStack<T> Cons(T head, ImmutableStack<T> tail)
{
return new ImmutableStack<T>(head, tail);
}
public static ImmutableStack<T> Reverse(ImmutableStack<T> s)
{
ImmutableStack<T> res = null;
while (s != null)
{
res = Cons(s.Head, res);
s = s.Tail;
}
return res;
}
}
class Program
{
static void AwesomeRecursion(int toDepth, int start, int max, ImmutableStack<int> indices)
{
if (toDepth < 0)
{
throw new ArgumentException("toDepth should be >= 0");
}
else if (toDepth == 0)
{
Console.Write("indices: ");
indices = ImmutableStack<int>.Reverse(indices);
while (indices != null)
{
Console.Write("{0}, ", indices.Head);
indices = indices.Tail;
}
Console.WriteLine();
}
else
{
for (int i = start; i < max; i++)
{
AwesomeRecursion(toDepth - 1, i + 1, max, ImmutableStack<int>.Cons(i, indices));
}
}
}
static void Main(string[] args)
{
AwesomeRecursion(4, 1, 10, null);
Console.WriteLine("Done");
Console.ReadKey(true);
}
}
We keep the indices on an immutable stack since it makes backtracking so much easier than mutable stacks or queues.