Difficulties with Binary Search Tree with Generics Implementation - java

I'm having an issue with implementing this BinarySearchTree listed below. For some context, I'm creating a binary search tree based off of an interface that requires generics and a comparable key.I think that there is a logic error in the code that is stumping me and it's in the insert method in the BinarySearchTree, but I'm not 100% sure.
Below is the class for my Node, which is used in my BST.
public class MyNodeClass<Key extends Comparable<Key>, Value>{
private Key key;
private Value value;
private MyNodeClass<Key,Value> left = null;
private MyNodeClass<Key,Value> right = null;
public MyNodeClass(Key key, Value val)
{
this.key = key;
this.value = val;
}
public void setKey(Key key){
this.key = key;
}
public void setValue(Value value){
this.value = value;
}
public Key getKey(){
return this.key;
}
public Value getValue(){
return this.value;
}
public void setLeft(MyNodeClass<Key, Value> l){
this.left = l;
}
public void setRight(MyNodeClass<Key, Value> r){
this.right = r;
}
public MyNodeClass<Key,Value> getLeft(){return this.left;}
public MyNodeClass<Key,Value> getRight(){return this.right;}
public int compareTo(Key that){
return(this.getKey().compareTo(that));
}
}
public class MyBinarySearchTree<Key extends Comparable<Key>, Value> implements BinarySearchTree<Key,Value> {
private MyNodeClass<Key, Value> root;
public MyBinarySearchTree(){
root = null;
}
#Override
public boolean isEmpty() {
return root == null;
}
#Override
public Value insert(Key key, Value val) {
MyNodeClass<Key,Value> newNode = new MyNodeClass<Key,Value>(key,val);
newNode.setKey(key);
newNode.setValue(val);
if(root==null){
root = newNode;
return(newNode.getValue());
}
else{
MyNodeClass<Key,Value> current = newNode;
MyNodeClass<Key,Value> parent;
while(true){
{
parent = current;
if(current.compareTo(key) == 1)
{
current = current.getLeft();
if(current == null)
{
parent.setLeft(newNode);
return parent.getLeft().getValue();
}
}
else if(current.compareTo(key) == -1){
current = current.getRight();
if(current == null)
{
parent.setRight(newNode);
return parent.getRight().getValue();
}
}
else{
if(current.compareTo(key) == 0){
current.setKey(key);
current.setValue(val);
return current.getValue();
}
}
}
}
}
}
#Override
public Value find(Key key) {
MyNodeClass<Key, Value> current = root;
while (current.compareTo(key) != 0)
{
if (current.compareTo(key) == 1)
{
current = current.getLeft();
} else {
current = current.getRight();
}
if(current == null)
return null;
}
return current.getValue();
}
#Override
public Value delete(Key key) {
MyNodeClass<Key,Value> current = root;
MyNodeClass<Key,Value> parent = root;
boolean isLeftChild = true;
while(current.compareTo(key) != 0) {
parent = current;
if (current.compareTo(key) == 1) {
isLeftChild = true;
current = current.getLeft();
} else {
isLeftChild = false;
current = current.getRight();
}
if(current == null)
return null;
}
if(current.getLeft() == null && current.getRight() == null) {
if (current == root) {
root = null;
} else if (isLeftChild) {
parent.setLeft(null);
} else{
parent.setRight(null);
}
return current.getValue();
}
else if(current.getRight() == null)
{
if(current == root) {
root = current.getLeft();
}
else if(isLeftChild) {
parent.setLeft(current.getLeft());
}
else{
parent.setRight(current.getLeft());
}
return current.getValue();
}
else if(current.getLeft() == null)
{
if(current == root)
root = current.getRight();
else if(isLeftChild)
parent.setLeft(current.getRight());
else
parent.setRight(current.getRight());
return current.getValue();
}
else
{
MyNodeClass<Key,Value> successor = getSuccessor(current);
if(current == root)
root = successor;
else if(isLeftChild)
parent.setLeft(successor);
else
parent.setRight(successor);
successor.setLeft(current.getLeft());
return current.getValue();
}
}
#Override
public String stringLevelOrder() {
return(LevelOrder(root));
}
private MyNodeClass<Key,Value> getSuccessor(MyNodeClass<Key,Value> deleteNode)
{
MyNodeClass<Key,Value> successorParent = deleteNode;
MyNodeClass<Key,Value> successor = deleteNode;
MyNodeClass<Key,Value> current = deleteNode.getRight();
while(current != null)
{
successorParent = successor;
successor = current;
current = current.getLeft();
}
if(successor != deleteNode.getRight())
{
successorParent.setLeft(successor.getRight());
successor.setRight(deleteNode.getRight());
}
return successor;
}
public static void main(String[] args)
{
MyBinarySearchTree<Double, MyStudent> BST = new MyBinarySearchTree<Double, MyStudent>();
MyStudent myStud1 = new MyStudent();
MyStudent myStud2 = new MyStudent();
MyStudent myStud3 = new MyStudent();
MyStudent myStud4 = new MyStudent();
MyStudent myStud5 = new MyStudent();
myStud1.init("Clarise", 1.1);
myStud2.init("Christopher", 1.2);
myStud3.init("John", 1.3);
myStud4.init("Chloe", 1.4);
myStud5.init("Goo", 1.5);
System.out.println(BST.insert(myStud1.getGPA(), myStud1));
System.out.println(BST.insert(myStud2.getGPA(), myStud2));
System.out.println(BST.insert(myStud3.getGPA(), myStud3));
System.out.println(BST.insert(myStud4.getGPA(), myStud4));
System.out.println(BST.insert(myStud5.getGPA(), myStud5));
System.out.println("Delete Key 1.0: " +BST.delete(1.3));
System.out.println("Delete Key 1.4: " +BST.delete(1.4));
System.out.println("Is Empty?: " +BST.isEmpty());
System.out.print("Find 3.9: "+ BST.find(3.9));
}
}
The result of the main is the following:
{Clarise:1.1}
{Christopher:1.2}
{John:1.3}
{Chloe:1.4}
{Goo:1.5}
Delete Key 1.0: null
Delete Key 1.4 null
Is Empty?: false
Find 3.9: null
I'm not entirely sure what the issue is and I've had some help from others, however they can't find the problem. Hoping that someone else can see something that we don't see.

In your insert method, after you've checked that root is not null, you are inserting newNode into the newNode instead of inserting it into the root.
This:
MyNodeClass<Key,Value> current = newNode;
MyNodeClass<Key,Value> parent;
Should be:
MyNodeClass<Key,Value> current = root;
MyNodeClass<Key,Value> parent;
P.S. any kind of testing would show you the problem with your insert within a minute. You could write a size() method and see that your inserts are not working, you could write a toString() method and see the state of the tree, finally you could debug.

MyNodeClass<Key,Value> current = newNode;
There is problem here.
If a tree is not empty, then your "current" should begin at root node. What you done is insert "newNode" to "newNode".
Change the code to be:
MyNodeClass<Key,Value> current = root;

Related

deleting a node from a binary search tree in java

I am making a boolean method that Deletes an element from the binary tree,
Returns true if the element is deleted successfully
, and Returns false if the element is not in the tree. The issue that I am having is that for some reason it is not deleting the node sometimes. I just want to know if I am doing anything wrong, thanks in advance.
here is my code:
public boolean delete(E e) {
BSTDelete<E> d = new BSTDelete<E>();
boolean deleted = d.delete(e, root);
if (deleted)
size -= 1;
return deleted;
}
public class BSTDelete<E extends Comparable<E>> {
public boolean delete(E e, TreeNode<E> root) {
if (root == null) {
return false;
}
if (e == root.element) {
if (root.right == null && root.left == null) {
root = null;
} else if (root.right == null) {
root = root.left;
} else if (root.left == null) {
root = root.right;
} else
root.element = minValue(root.left);
delete(root.element, root.left);
// Delete the inorder successor
} else if (e.compareTo(root.element) < 0) {
delete(e, root.left);
} else {
delete(e, root.right);
}
return true;
}
E minValue(TreeNode<E> root) {
E minv = root.element;
while (root.right != null) {
minv = root.right.element;
root = root.right;
}
return minv;
}
}
here is a test that keeps failing. The second assertEquals says that i.next() is "Beatrice" and not "Carl"
BST <String>b = new BST<String>();
b.insert("Arthur");
b.insert("Beatrice");
b.insert("Carl");
b.insert("Dagmar");
b.delete("Beatrice");
Iterator <String> i = b.iterator();
assertEquals(i.next(), "Arthur");
assertEquals(i.next(), "Carl");
assertEquals(i.next(), "Dagmar");
}
and here is my BSTInorderIterator class:
public class BSTInorderIterator<E extends Comparable<E>> implements
java.util.Iterator<E> {
int current = 0;
ArrayList<E> list = new ArrayList<E>();
private TreeNode<E> root;
public BSTInorderIterator(TreeNode<E> root) {
list = new ArrayList<E>();
inorder(root);
}
/** Inorder traversal from the root */
public void inorder() {
inorder(root);
}
/** Inorder traversal from a subtree */
public void inorder(TreeNode<E> root) {
if (root.left != null)
inorder(root.left);
list.add(root.element);
if (root.right != null)
inorder(root.right);
}
#Override
/** More elements for traversing? */
public boolean hasNext() {
return current < list.size();
}
#Override
/** Get the current element and move to the next */
public E next() {
return list.get(current++);
}
#Override
/** Remove the current element */
public void remove() {
// to do: make this work correctly
}
The delete method inside the class BSTDelete is a recursive method, however you're never returning the recursive method calls. Therefore your delete method will only ever return false when you call it with a like d.delete(e, root) where root is null.
For example even though delete(e, root.left) might return false because root.left is null your original method call will return true since you don't return the result of delete(e, root.left).
To fix this add return when you're calling the method recursively, this might only be a partial fix to your issue:
public boolean delete(E e, TreeNode<E> root) {
if (root == null) {
return false;
}
if (e == root.element) {
if (root.right == null && root.left == null) {
root = null;
} else if (root.right == null) {
root = root.left;
} else if (root.left == null) {
root = root.right;
} else
root.element = minValue(root.left);
return delete(root.element, root.left);
// Delete the inorder successor
} else if (e.compareTo(root.element) < 0) {
return delete(e, root.left);
} else {
return delete(e, root.right);
}
return true;
}

Doubly Linked List - RemoveFirst Method

I need help with following Code:
public boolean remove(Integer value) {
if (isEmpty()) {
throw new NoSuchElementException();
}
if (!isEmpty()) {
if (head == tail) {
head = tail = null;
}
} else {
}
size--;
return false;
}
And this is my task:
"removes the first occurrence of the specified value from this list"
It s a method of a Doubly Linked List.
So far I think I did correct but I am still missing the "else" part and I have no clue what to put inside...
I also have a class with a constructor and getter- and setter- methods.
Here is my node class:
public class ListElement {
private Integer value;
private ListElement next;
private ListElement prev;
public ListElement(ListElement prev, Integer value, ListElement next) {
this.value = value;
this.next = next;
this.prev = prev;
}
public Integer getValue() {
return value;
}
public ListElement getNext() {
return next;
}
public ListElement getPrev() {
return prev;
}
public void setValue(Integer value) {
this.value = value;
}
public void setNext(ListElement next) {
this.next = next;
}
public void setPrev(ListElement prev) {
this.prev = prev;
}
}
I am assuming by the function signature that you want to delete the element with the specific value. You need to find that node and remove it:
public boolean remove(Integer value) {
if (isEmpty()) {
throw new NoSuchElementException();
}
ListElement found = head;
// Try to find it
while (null != found && !found.value.equals(value)) {
found = found.next;
}
// Not found?
if (null == found) {
throw new NoSuchElementException();
}
// Found. Unlink
if (found.prev != null) found.prev.next = found.next;
else head = found.next;
if (found.next != null) found.next.prev = found.prev;
else tail = found.prev;
size--;
return true;
}
Firstly, this if should be removed as you already test for empty
if (!isEmpty()) {
if (head == tail) {
head = tail = null;
}
} else {
}
Then you can process like:
public boolean remove(Integer value) {
if (isEmpty()) {
throw new NoSuchElementException();
}
if (head == tail) {
if (head.getValue() == value) {
head = tail = null;
} else {
// Not found, return false
size--;
return false;
}
}
ListElement current = head;
while (current != null) {
if (current.getValue() == value) {
// Found
if (current.getPrev() == null) {
// current node is head node
head = current.getNext();
current.setPrev(null);
} else if (current.next() == null) {
// current node is tail node
tail = current;
current.setNext(null);
} else {
// Current node is in the middle
ListElement prev = current.getPrev();
ListElement next = current.getNext();
prev.setNext(next);
next.setPrev(prev);
}
size--;
return true;
}
}
// Not found
size--;
return false;
}

Problems with Binary Tree node removal Java

I wanted to try and implement my own BST as an exercise, but I am stuck on the node removal. I cannot figure out why it doesn't work in some cases. I took the algorithm from a book, but when I test it with random elements, there are cases in which it does not remove the element, or even messes up their order so they are no longer sorted. What am I doing wrong and what would be a better way to accomplish this?
NOTE: All of the println() statements in the methods are there only for debugging purposes
class TreeNode<T extends Comparable<T>> {
T data;
TreeNode<T> left;
TreeNode<T> right;
TreeNode<T> parent;
TreeNode(T data) {
this.data = data;
}
boolean hasBothChildren() {
return hasLeftChild() && hasRightChild();
}
boolean hasChildren() {
return hasLeftChild() || hasRightChild();
}
boolean hasLeftChild() {
return left != null;
}
boolean hasRightChild() {
return right != null;
}
boolean isLeftChild() {
return this.parent.left == this;
}
boolean isRightChild() {
return this.parent.right == this;
}
}
public class BinaryTreeSet<T extends Comparable<T>> {
private TreeNode<T> root;
private void makeRoot(T element) {
TreeNode<T> node = new TreeNode<T>(element);
root = node;
}
private TreeNode<T> find(T element) {
TreeNode<T> marker = root;
TreeNode<T> found = null;
while (found == null && marker != null) {
int comparator = (marker.data.compareTo(element));
if (comparator > 0)
marker = marker.left;
else if (comparator < 0)
marker = marker.right;
else
found = marker;
}
return found;
}
private TreeNode<T> max(TreeNode<T> root) {
TreeNode<T> currentMax = root;
while (currentMax.hasRightChild()) {
currentMax = currentMax.right;
}
return currentMax;
}
// returns the inorder predecessor of node
private TreeNode<T> predecessor(TreeNode<T> node) {
return max(node.left);
}
// removes a given node with 0 or 1 children
private void removeNode(TreeNode<T> node) {
if (!node.hasChildren()) {
System.out.println("node with no children");
if (node.isLeftChild())
node.parent.left = null;
else
node.parent.right = null;
}
else {
System.out.println("node with 1 child");
if (node.isRightChild()) {
if (node.hasLeftChild())
node.parent.right = node.left;
else if (node.hasRightChild())
node.parent.right = node.right;
}
else if (node.isLeftChild()) {
if (node.hasLeftChild())
node.parent.left = node.left;
else if (node.hasRightChild())
node.parent.left = node.right;
}
}
node = null;
}
public BinaryTreeSet() {
root = null;
}
public void addElement(T element) {
if (root == null)
makeRoot(element);
else {
TreeNode<T> marker = root;
TreeNode<T> node = new TreeNode<T>(element);
boolean done = false;
while(!done) {
int comparator = marker.data.compareTo(element);
if (comparator > 0) {
if (marker.hasLeftChild())
marker = marker.left;
else {
marker.left = node;
done = true;
}
}
else if (comparator < 0) {
if (marker.hasRightChild())
marker = marker.right;
else {
marker.right = node;
done = true;
}
}
else
return;
node.parent = marker;
}
}
}
public boolean contains(T element) {
boolean found = (find(element) == null)? false : true;
return found;
}
public boolean removeElement(T element) {
TreeNode<T> node = find(element);
if (node == null)
return false;
// removal of a node with no children
if (!node.hasChildren()) {
if (node.isLeftChild()) {
node.parent.left = null;
}
else if (node.isRightChild()) {
node.parent.right = null;
}
}
// removal of a node with both children
else if (node.hasBothChildren()) {
TreeNode<T> pred = predecessor(node);
T temp = pred.data;
pred.data = node.data;
node.data = temp;
removeNode(pred);
}
// removal of a node with only 1 child
else {
if (node.isRightChild()) {
if (node.hasLeftChild())
node.parent.right = node.left;
else if (node.hasRightChild())
node.parent.right = node.right;
}
else if (node.isLeftChild()) {
if (node.hasLeftChild())
node.parent.left = node.left;
else if (node.hasRightChild())
node.parent.left = node.right;
}
}
node = null;
System.out.println("item removed: " + !contains(element));
return true;
}
}
please add following Method into BinaryTreeSet Class and call it,
which will show you current element list with Left/Right prefix.
boolean rootOncePrint = true;
public void printAllTree(TreeNode<T> startNode){
if(startNode == null) return;
//System.out.println(startNode.data);
if(rootOncePrint){
System.out.println("Root : " + startNode.data);
rootOncePrint = false;
}
if(startNode.hasChildren()){
if(startNode.hasLeftChild()){
printAllTree(startNode.left);
}
if(startNode.hasRightChild()){
printAllTree(startNode.right);
}
}
if(startNode != root){
T parentValue = startNode.parent.data;
T dataValue = startNode.data;
System.out.println(startNode.data + ((parentValue.compareTo(dataValue) > 0)?"L":"R"));
}
}
After Add this code, try to add/remove element into BinaryTreeSet so
you will get to know what's going on.
Found the bug that was causing me headaches. The problem was in the cases where I remove nodes with 0 or 1 child. I was not updating their parent nodes, so that messed up with the code. So, instead of, for example
if (node.hasLeftChild())
node.parent.right = node.left;
I should have written
if (node.hasLeftChild()) {
node.parent.left = node.left;
node.left.parent = node.parent;
}
in all cases where I deal with a single child. Also, I forgot to update the root, when the root is the target of the removeElement() function.
However, as it currently stands, I feel I have a lot of repetition in the code. I am yet to come up with a more elegant solution.
EDIT: There are other minor bugs as well, mainly in the isRightChild() and isLeftChild() functions, resulting in NullPointerException if the node in question does not have a parent.

Implementing and visualizing a binary tree in java

i had to implement a binary tree pictured on this file
together with the class Diagramm and binary tree for orientation.
So following the text and the Pictures i have to implement a constructor, a get- and insert method for this binary tree.
public class BinaryTree {
private Node root = null;
private static class Node {
private Integer key;
private String value;
private Node left = null;
private Node right = null;
public Node(Integer key, String value) {
this.key = key;
this.value = value;
}
}
public boolean insert(Integer key, String value) {
if (root == null) {
root = new Node(key, value);
return true;
} else {
return insert(root, key, value);
}
}
private boolean insert(Node node, Integer key, String value) {
if (key.equals(node.key)) {
// duplicate
return false;
} else if (key < node.key) {
if (node.left == null) {
node.left = new Node(key, value);
return true;
} else {
return insert(node.left, key, value);
}
} else if (key > node.key) {
if (node.right == null) {
node.right = new Node(key, value);
return true;
} else {
return insert(node.right, key, value);
}
}
return false;
}
// not tested, crass assumptions, public domain
public String get(Integer key) {
return get(root, key); // start search from the root.
}
public String get(Node node, Integer key) {
String result = null; // Assume key is not found
if (node.key.equals(key)) { // Key matches? This is the result.
return node.value;
} else {
if (key < node.key && node.left != null) { // key is lower than
// current node,
// and there is a left
// branch, keep
// search from there.
result = get(node.left, key);
} else if (key > node.key && node.right != null) { // key is greater
// than current
// node,
// and there is
// a left
// branch,
// keep search
// from there.
// The key >
// node.key is
// arguably
// redundant.
result = get(node.right, key);
}
}
return result;
}
How can i implement a correct main function for testing? And on top i have to visualize the binary tree with help of graphviz and adding a method in the node class which creates a string for the dot-code. How does it work with Eclipses?
The get method will start at a specific node within the tree, and check whether that node itself meets the criteria. If it does, it returns the value. If not, it will defer to the appropriate branch and continue searching.
// not tested, crass assumptions, public domain
public String get(Integer key) {
return get(root, key); // start search from the root.
}
public String get(Node node, Integer key) {
String result = null; // Assume key is not found
if (node.key.equals(key)) { // Key matches? This is the result.
return node.value;
} else {
if (key < node.key && node.left != null) { // key is lower than current node,
// and there is a left branch, keep
// search from there.
result = get(node.left, key);
} else if (key > node.key && node.right != null) { // key is greater than current node,
// and there is a left branch,
// keep search from there.
// The key > node.key is arguably
// redundant.
result = get(node.right, key);
}
}
return result;
}
If you choose procedural approach, right way to do things will be that:
public class BinaryTree {
private Node root = null;
private static class Node {
private Integer key;
private String value;
private Node left = null;
private Node right = null;
public Node(Integer key, String value) {
this.key = key;
this.value = value;
}
}
public boolean insert(Integer key, String value) {
if (root == null) {
root = new Node(key, value);
return true;
} else {
return insert(root, key, value);
}
}
private boolean insert(Node node, Integer key, String value) {
if (key.equals(node.key)) {
// duplicate
return false;
} else if (key < node.key) {
if (node.left == null) {
node.left = new Node(key, value);
return true;
} else {
return insert(node.left, key, value);
}
} else if (key > node.key) {
if (node.right == null) {
node.right = new Node(key, value);
return true;
} else {
return insert(node.right, key, value);
}
}
return false;
}
}
Now compare it to OOP approach and choose, which one you like more:
public class BinaryTree {
private Node root = null;
private static class Node {
private Integer key;
private String value;
private Node left = null;
private Node right = null;
public Node(Integer key, String value) {
this.key = key;
this.value = value;
}
private boolean insert(Integer key, String value) {
if (key.equals(this.key)) {
// duplicate
return false;
} else if (key < this.key) {
if (left == null) {
left = new Node(key, value);
return true;
} else {
return left.insert(key, value);
}
} else if (key > this.key) {
if (right == null) {
right = new Node(key, value);
return true;
} else {
return right.insert(key, value);
}
}
return false;
}
}
public boolean insert(Integer key, String value) {
if (root == null) {
root = new Node(key, value);
return true;
} else {
return root.insert(key, value);
}
}
}
Solution is simple. For insert operation:
If there is no root in the tree yet, create one.
Otherwise add a new value to the root node.
Inserting a value to some node (starting from root one):
If node's key equals to the inserted key => we have a duplicate and won't proceed any further.
If inserted key is lesser than node's key, do:
If there is no left subtree, create a new node and assign it as a left child.
If there is already a left subtree, recursively add new (key, value) to it.
If inserted key is greater than node's key, do: (by analogy with #2)

How to check if member exists

So i have implemented the insert method and it works just fine but my problem is how to check whether a member is already in the list or not,i want the program to check if the member is already in the list but the checker doesn't work. i want the program to put the member in team1 if the member is included in the list and Display "member does not exist" if the member is not on the list. I made a check method but it doesn't work. I am new in Programming and i really need help. Please enlighten me with your knowledge.
class Node
{
protected String info;
protected Node next;
public Node(String value)
{
info = value;
next = null;
}
}
class LinkedList
{
private Node head;
private int count;
public LinkedList()
{
head = null;
count = 0;
}
public void insert( String name)
{
Node a = new Node(name);
a.next = null;
count++;
if (head == null)
{
head = a;
return;
}
for(Node cur = head; cur != null; cur = cur.next)
{
if (cur.next == null)
{
cur.next = a;
return;
}
}
}
public void checker(String name)
{
for(Node cur = head; cur != null; cur = cur.next)
{
if(cur.info == name)
{
insertteam1(name);
System.out.print("OK");
}
else
{
System.out.print("member does not exist");
}
}
}
public void insertteam1(String name)
{
Node b = new Node(name);
b.next = null;
count++;
if (head == null)
{
head = b;
return;
}
for(Node cur = head; cur != null; cur = cur.next)
{
if (cur.next == null)
{
cur.next = b;
return;
}
}
}
In the code below,
if(cur.info == name){ // }
you are comparing the string info using == which is not the right way to compare strings in java.
Use
if(cur.info.equals(name)){ // }
or
use if(cur.info.equalsIgnoreCase(name)){ // } if you want to do case insensitive compare.

Categories