I've been trying to create a integer binary search tree with Java and for some reason, I've been going wrong with adding new nodes to the tree.
Here is the NODE class.
class NODE
{
NODE left = null, right = null;
int info;
public NODE(int x)
{
info = x;
}
}
and here's the BST(Binary Seatch Tree) class with the insert() method.
class BST
{
NODE tree = null;
public void insert(int x)
{
NODE node = new NODE(x);
NODE temp = tree;
while(true)
{
if(temp == null)
{
temp = node;
break;
}
else if(temp.info > x) temp = temp.left;
else temp = temp.right;
}
}
//other methods present here
}
For reasons that I could not figure out, the insert() method is going wrong.
The object tree carries null in it even after the insert() method is called.
Can you find something spotty in the code?
Thanks!
Use a recursive insert method in the NODE class (instead of utilizing an infinite loop as you did):
public void insert(int x) {
if(x < this.info) {
if(this.left == null)
this.left = new NODE(x);
else
this.left.insert(x);
}
else {
if(this.right == null)
this.right = new NODE(x);
else
this.right.insert(x);
}
}
And your BST class would have the following insert method (simply calls the other insert method):
public void insert(int x) {
if(tree == null)
tree = new NODE(x);
else
tree.insert(x);
}
The main insert method is in the NODE class because it must recursively call itself on nodes within the tree.
Of course tree remains null - you don't assign anything to this field.
After temp = tree; and temp = node; only temp is changed, not tree.
The insert() method should insert the child of a node into the tree, calling an already declared Node as a parameter. e.g.:
//Returns true/false depending on whether the insert is successful
public boolean insert(int x, Node node, boolean leftChild) {
if (node == null) return false;
Node child = new Node(x);
if (leftChild) {
if (node.left != null) return false;
node.left = child;
} else {
if (node.right != null) return false;
node.right = child;
}
return true;
}
Related
I am trying to insert in a binary search tree using recursion and then print it preorderly using this specific code, but I have only root as output,why?Is this because each time stack(after each call) is popping off thus removing new nodes?(This is a java code)
class node{
int data;
node left;
node right;
node(int key){
data = key;
left = right = null;
}
}
class bst{
node root;
node temp;
node last;
bst(){
root = null;
}
bst(int key){
root = new node(key);
}
void Insert(node r,int value){
temp = r;
if(temp == null){
if(root == null){
root = new node(value);
root.data = value;
return;
}
temp = new node(value);
temp.data = value;
return;
}
else{
if(value > temp.data){
Insert(temp.right,value);
return;
}
else{
Insert(temp.left,value);
return;
}
}
}
}
class test{
static void in_order(node root){
if(root == null){
return;
}
in_order(root.left);
System.out.println(root.data+" ");
in_order(root.right);
}
public static void main(String[] args){
bst tree = new bst();
tree.Insert(tree.root,45);
tree.Insert(tree.root,39);
tree.Insert(tree.root,12);
tree.Insert(tree.root,59);
test.in_order(tree.root);
}
}
The reason you are only getting a single integer for an output is because the first Insert call correctly adds the element to the tree, but subsequent calls fail because you overwrite the data member temp to null when you recursively insert to the left or right. Thus the second branch of your first if statement never gets executed.
You don't actually need the variable temp here. A common convention is to have a private, recursive member function that takes the root of the tree as a parameter returns the modified tree, and assign the return value to root in a public member function.
public void Insert(int value) {
root = Insert(root, value);
}
private node Insert(node r, int value) {
if (r == null) {
r = new node(value);
}
else if (value > r.data) {
r.right = Insert(r.right, value);
}
else {
r.left = Insert(r.left, value);
}
return r;
}
This means that you only have to call it like tree.Insert(x).
I was doing an assignment in which I'm supposed to create a binary tree and define given functions from its abstract superclass (AbstractBinaryTree.java).
While working on a function called getNumbers() which is basically going to traverse through the whole tree whilst adding values from each node to an array list which it returns. There seems to be a null pointer in one of my if statements.
AbstractBinaryTree.java
import java.util.ArrayList;
public abstract class AbstractBinaryTree
{
protected Node root;
protected int sizeOfTree;
public AbstractBinaryTree()
{
root = null;
sizeOfTree = 0;
}
public int size(){ return sizeOfTree; }
/** compute the depth of a node */
public abstract int depth(Node node);
/** Check if a number is in the tree or not */
public abstract boolean find(Integer i);
/** Create a list of all the numbers in the tree. */
/* If a number appears N times in the tree then this */
/* number should appear N times in the returned list */
public abstract ArrayList<Integer> getNumbers();
/** Adds a leaf to the tree with number specifed by input. */
public abstract void addLeaf(Integer i);
/** Removes "some" leaf from the tree. */
/* If the tree is empty should return null */
public abstract Node removeLeaf();
// these methods are only needed if you wish
// use the TreeGUI visualization program
public int getheight(Node n){
if( n == null) return 0;
return 1 + Math.max(
getheight(n.getLeft()) , getheight(n.getRight())
);
}
public int height(){ return getheight(root); }
}
Node.java File.
public class Node{
protected Integer data;
protected Node left;
protected Node right;
public Node(Integer data)
{
this.data = data;
this.left = this.right = null;
}
public Node(Integer data, Node left, Node right){
this.data = data;
this.left = left;
this.right = right;
}
public Integer getData(){ return this.data; }
public Node getLeft(){ return this.left; }
public Node getRight(){ return this.right; }
public void setLeft(Node left){ this.left = left; }
public void setRight(Node right){ this.right = right; }
public void setData(Integer data){ this.data = data; }
}
BinaryTree.java
import java.util.ArrayList;
import java.util.*;
// Student Name: Adrian Robertson
// Student Number: 101020295
//
// References: Collier, R. "Lectures Notes for COMP1406C- Introduction to Computer Science II" [PDF documents]. Retrieved from cuLearn: https://www.carleton.ca/culearn/(Winter2016).//
// References: http://codereview.stackexchange.com/questions/13255/deleting-a-node-from-a-binary-search-tree
// http://www.algolist.net/Data_structures/Binary_search_tree/Removal
// http://www.geeksforgeeks.org/inorder-tree-traversal- without-recursion-and-without-stack/
public class BinaryTree extends AbstractBinaryTree
{
protected Node root = new Node(12);
public static BinaryTree create()
{
BinaryTree tempTree = new BinaryTree();
//creating all the nodes
Node temp10 = new Node(10);
Node temp40 = new Node(40);
Node temp30 = new Node(30);
Node temp29 = new Node(29);
Node temp51 = new Node(51);
Node temp61 = new Node(61);
Node temp72 = new Node(72);
Node temp31 = new Node(31);
Node temp32 = new Node(32);
Node temp42 = new Node(42);
Node temp34 = new Node(34);
Node temp2 = new Node(2);
Node temp61x2 = new Node(61);
Node temp66 = new Node(66);
Node temp3 = new Node(3);
Node temp73 = new Node(73);
Node temp74 = new Node(74);
Node temp5 = new Node(5);
//setting up the tree
if (tempTree.root.getData() == null)
{
tempTree.root.setData(12);
tempTree.root.setLeft(temp10);
tempTree.root.setRight(temp40);
}
temp10.setLeft(temp30);
temp30.setRight(temp29);
temp29.setRight(temp51);
temp51.setLeft(temp61);
temp51.setRight(temp72);
temp40.setLeft(temp31);
temp31.setLeft(temp42);
temp31.setRight(temp34);
temp34.setLeft(temp61x2);
temp61x2.setLeft(temp66);
temp61x2.setRight(temp73);
temp40.setRight(temp32);
temp32.setRight(temp2);
temp2.setLeft(temp3);
temp3.setRight(temp74);
temp74.setLeft(temp5);
return tempTree;
}
public int depth(Node node)
{
Node current = this.root;
int counter = 1;
while(node != current)
{
if (node.getData() > current.getData())
current = current.getRight();
if (node.getData() < current.getData())
current = current.getLeft();
}
return counter;
}
public boolean find(Integer i)
{
boolean found = false;
Node current = this.root;
if (i == current.getData())
found = true;
while (i != current.getData())
{
if (i > current.getData())
current = current.getRight();
if (i < current.getData())
current = current.getLeft();
if (i == current.getData())
found = true;
}
return found;
}
public ArrayList<Integer> getNumbers()
{
ArrayList<Integer> temp = new ArrayList<Integer>();
Node current = this.root;
Node Pre = new Node(null);
while (current.getData() != null )
{
if (current.getLeft().getData() == null)
{
temp.add(current.getData());
current = current.getRight();
}
else
{
/* Find the inorder predecessor of current */
Pre = current.getLeft();
while(Pre.getRight() != null && Pre.getRight() != current)
Pre = Pre.getRight();
/* Make current as right child of its inorder predecessor */
if (Pre.getRight() == null)
{
Pre.setRight(current);
current = current.getLeft();
}
/* Revert the changes made in if part to restore the original tree i.e., fix the right child of predecssor */
else
{
Pre.setRight(null);
temp.add(current.getData());
current = current.getRight();
}/* End of if condition Pre.right == NULL */
}/* End of if condition current.left == NULL*/
}/*End of while */
Collections.sort(temp);
return temp;
}
public void addLeaf(Integer i)
{
insert(this.root, i);
}
public static void insert(Node node, int value) //insert a node Based on provided argument where node is the root of tree
{
if (node == null)
{
Node first = new Node(value);
node = first;
}
else if (value < node.getData())
{
if (node.left != null)
{
insert(node.left, value);
}
else
{
System.out.println(" > Inserted " + value + " to left of node " + node.getData());
Node newNode = new Node(value);
node.left = newNode;
}
}
else if (value > node.getData())
{
if (node.right != null)
{
insert(node.right, value);
}
else
{
System.out.println(" > Inserted " + value + " to right of node " + node.getData());
Node newNode = new Node(value);
node.right = newNode;
}
}
}
public Node removeLeaf()
{
Node tempA = new Node(61); //create a new node with that value
deleteNodeBST(this.root, 61); //delete the node containing that leaf value
return tempA; //return the copy of that node
}
//delete given node with given value
public boolean deleteNodeBST(Node node, int data) {
ArrayList<Integer> temp = this.getNumbers();
if (node == null) {
return false;
}
if (node.getData() == data) {
if ((node.getLeft() == null) && (node.getRight() == null)) {
// leaf node
node = null;
return true;
}
if ((node.getLeft() != null) && (node.getRight() != null)) {
// node with two children
node.setData(temp.get(0));
return true;
}
// either left child or right child
if (node.getLeft() != null) {
this.root.setLeft(node.getLeft());
node = null;
return true;
}
if (node.getRight() != null) {
this.root.setRight(node.getRight());
node = null;
return true;
}
}
this.root = node;
if (node.getData() > data) {
return deleteNodeBST(node.getLeft(), data);
} else {
return deleteNodeBST(node.getRight(), data);
}
}
public static void main(String args[])
{
BinaryTree myTree = new BinaryTree();
myTree.create();
System.out.println(myTree.getNumbers());
}
}
The create function creates a binary tree and returns that binary tree. This is the predefined binary tree that I was supposed to create according to assignment guidelines. I understand that the tree values are not organised properly as they would be in a proper binary tree. Is that was causes the null pointer during traversal? Cause the traversal is taylored to work for a proper Binary tree.
In class BinaryTree, you initialize the left and right of your root node only if the haven't data. But the root node is create with data...
You should invert the condition in :
//setting up the tree
if (tempTree.root.getData() == null)
And add a test in getNumbers() :
if (current.getLeft() == null || current.getLeft().getData() == null)
In the BinaryTree class, getNumbers() method and while loop. Maybe your problem is here:
if (current.getLeft().getData() == null) {
temp.add(current.getData());
current = current.getRight();
}
When you call current.getLeft(), it will return null when the left Node is null. And then, you call getData() it will throw a NullPointerException. If you're not sure that it always not null check it before you call any methods of it. Example you can change the if statement to:
if (current.getLeft() != null && current.getLeft().getData() == null) {
temp.add(current.getData());
current = current.getRight();
}
Or:
Node left = current.getLeft();
if (left == null) {
//TODO something here
} else if (left.getData() == null) {
temp.add(current.getData());
current = current.getRight();
}
Please update your getNumbers - method accordingly,
You need to put right checks before work with reference type.
public ArrayList<Integer> getNumbers()
{
ArrayList<Integer> temp = new ArrayList<Integer>();
Node current = this.root;
Node Pre = new Node(null);
while (current != null && current.getData() != null ) // Fix here... Add : current != null
{
if (current.getLeft() != null && current.getLeft().getData() == null) // Fix here... Add : current.getLeft() != null
{
temp.add(current.getData());
current = current.getRight();
}
else
{
/* Find the inorder predecessor of current */
Pre = current.getLeft();
while(Pre != null && Pre.getRight() != null && Pre.getRight() != current) // Fix here... Add : Pre != null
Pre = Pre.getRight();
/* Make current as right child of its inorder predecessor */
if (Pre != null && Pre.getRight() == null) // Fix here... Add : Pre != null
{
Pre.setRight(current);
current = current.getLeft();
}
/* Revert the changes made in if part to restore the original tree i.e., fix the right child of predecssor */
else
{
if(Pre != null){ // Fix here... Add : Pre != null
Pre.setRight(null);
}
temp.add(current.getData());
current = current.getRight();
}/* End of if condition Pre.right == NULL */
}/* End of if condition current.left == NULL*/
}/*End of while */
Collections.sort(temp);
return temp;
}
I'm writing a code for implementing BST in java. My insert, search, search for inorder successor, inorder traversal work fine but when I remove a node, it is not actually removed. Consider the simplest case where the node to be removed is a pendant node. Even if I set this node to null, it is still printed in inorder traversal after deletion. Can anyone please help? Thank you.
package pack_l;
class BSTNode
{
int key;
BSTNode left;
BSTNode right;
BSTNode(int key)
{
this.key = key;
this.left = this.right = null;
}
}
class BST
{
BSTNode root;
BST()
{
root = null;
}
/*insert a node at proper position*/
void insert(BSTNode n)
{
if(root == null)
root = n;
else
{
BSTNode node = root;
while(node != null)
{
if(node.key > n.key)
{
if(node.left == null)
{
node.left = n;
return;
}
else
node = node.left;
}
else
{
if(node.right == null)
{
node.right = n;
return;
}
else
node = node.right;
}
}/*End of while-loop*/
}
}
/*Search a node in the whole tree*/
BSTNode search(int val)
{
BSTNode node = root;
while(node != null)
{
if(node.key == val)
return node;
else if(node.key > val)
node = node.left;
else
node = node.right;
}
return null;
}
/*Remove a node from the tree*/
boolean remove(int val)
{
BSTNode delNode = search(val);
/*If the node is not in the BST*/
if(delNode == null)
return false;
/*If the node has no child*/
if(delNode.left == null && delNode.right == null)
delNode = null;
return true;
}
void inorder(BSTNode root)
{
if(root == null)
return;
inorder(root.left);
System.out.print(" " + root.key + " ");
inorder(root.right);
}
}
public class BSTree {
public static void main(String[] args) {
BST tree = new BST();
BSTNode n1 = new BSTNode(15);
tree.insert(n1);
System.out.println("Before:");
tree.inorder(tree.root);
tree.remove(15);
System.out.println("\nAfter:");
tree.inorder(tree.root);
}
}
Setting delnode = null does nothing: you have a local copy of the reference to a node, and you changed it to refer to null. That doesn't change the actual node in memory at all.
Instead, you must find its parent and set that parent's left or right reference (depending on which is the node to delete) to null.
I'm trying to implement a binary tree, but its just not taking the root. Any ideas? It looks like the root should be inserting fine, but I'm just getting a null when I print it. Am I trying to add only temporary nodes to the tree that don't "stick"?
public class tree {
public static void main(String args[]){
Treeb tree = new Treeb();
tree.add(10);
tree.add(20);
tree.add(2);
tree.add(6);
tree.printTree();
}
}
class Node{
int data;
Node left;
Node right;
public Node(int data){
this.data = data;
left = null;
right = null;
}
Node getLeft(){
return left;
}
Node getRight(){
return right;
}
}
class Treeb{
Node root;
Treeb(){
root = null;
}
void add(int n){
addNode(n, root);
}
void addNode(int n, Node vert){
if(vert == null){
vert = new Node(n);
}
else if(vert.left.data < n){
if(vert.left == null){
vert.left = new Node(n);
}
else{
addNode(n, vert.left);
}
}
else if(vert.right.data >= n){
if(vert.right == null){
vert.right = new Node(n);
}
else{
addNode(n,vert.right);
}
}
}
void printTree(){
if(root != null){
printChild(root);
}
System.out.println(root);
}
void printChild(Node leaf){
System.out.print(leaf.data);
if(leaf.left != null){
printChild(leaf.getLeft());
}
if(leaf.right != null){
printChild(leaf.getRight());
}
}
}
You are assigning vert a new reference, but not root, that's why it stays null.
Your method addNode(int, Node) isn't working.
First:
if(vert == null){
vert = new Node(n);
}
You're assigning the new node to a local variable. Thus, the new Node gets discarded at the end of the method.
Second:
}
else if(vert.left.data < n){
// code
}
else if(vert.right.data >= n){
vert.left and vert.rightcan be null, so you would get an NPE when vert is not null.
getLeft() and getRight() can (and will) return null sometime. You should make sure in your printChild() that leaf itself is not null. (You're probably getting NPE in if(leaf.left != null) since leaf is null), you might also want to reconsider your tree construction again, root is null in your case.
So this is my first java program, but I've done c++ for a few years. I wrote what I think should work, but in fact it does not. So I had a stipulation of having to write a method for this call:
tree.insertNode(value);
where value is an int.
I wanted to write it recursively, for obvious reasons, so I had to do a work around:
public void insertNode(int key) {
Node temp = new Node(key);
if(root == null) root = temp;
else insertNode(temp);
}
public void insertNode(Node temp) {
if(root == null)
root = temp;
else if(temp.getKey() <= root.getKey())
insertNode(root.getLeft());
else insertNode(root.getRight());
}
Thanks for any advice.
// In java it is little trickier as objects are passed by copy.
// PF my answer below.
// public calling method
public void insertNode(int key) {
root = insertNode(root, new Node(key));
}
// private recursive call
private Node insertNode(Node currentParent, Node newNode) {
if (currentParent == null) {
return newNode;
} else if (newNode.key > currentParent.key) {
currentParent.right = insertNode(currentParent.right, newNode);
} else if (newNode.key < currentParent.key) {
currentParent.left = insertNode(currentParent.left, newNode);
}
return currentParent;
}
Sameer Sukumaran
The code looks a little confusing with overloaded functions. Assuming member variables 'left' and 'right' to be the left child and right child of the BSTree respectively, you can try implementing it in the following way:
public void insert(Node node, int value) {
if (value < node.value)
{
if (node.left != null)
{
insert(node.left, value);
}
else
{
node.left = new Node(value);
}
}
else if (value > node.value)
{
if (node.right != null)
{
insert(node.right, value);
}
else
{
node.right = new Node(value);
}
}
}
........
public static void main(String [] args)
{
BSTree bt = new BSTree();
Node root = new Node(100);
bt.insert(root, 50);
bt.insert(root, 150);
}
You should have a look to this article. It helps to implement a tree structure and search, insert methods:
http://quiz.geeksforgeeks.org/binary-search-tree-set-1-search-and-insertion/
// This method mainly calls insertRec()
void insert(int key) {
root = insertRec(root, key);
}
/* A recursive function to insert a new key in BST */
Node insertRec(Node root, int key) {
/* If the tree is empty, return a new node */
if (root == null) {
root = new Node(key);
return root;
}
/* Otherwise, recur down the tree */
if (key < root.key)
root.left = insertRec(root.left, key);
else if (key > root.key)
root.right = insertRec(root.right, key);
/* return the (unchanged) node pointer */
return root;
}
You can use standard Integer (wrapper for primitive int) object instead of creating a new object type Node. On latest java Integer/int auto-boxing is supported. Hence your method insertNode(int key) can take in Integer argument too (ensure it is not null).
EDIT: Pls ignore above comment. I did not understand your real question. You will have to overload insertNode(). I think you are right.
but where is temp when you insertNode?? With your current implementation temp is lost if root is not null.
I think you want something like
root.getLeft().insertNode(temp);
and
root.getRight().insertNode(temp);
i.e. To insert the new Node (temp) to either the left or the right subtree.