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How to update the height of nodes when added or removed from a binary search tree?

I am trying to implement a getHeight method that has a o(1) time complexity. To do this I am aiming to assign every node their own height and to return the height of the root with the getHeight method. To do this I need to update the height of the nodes everytime I add or remove.
Thus, I chose to do this:
private void updateHeight(Node node)
{
if (node == null)
{
return;
}
updateHeight(node.left);
updateHeight(node.right);
this.helpHeight(node);
}
private void helpHeight(Node node)
{
if (this.isLeaf(node))
{
node.height = 0;
}
else if (node.left == null)
{
node.height = node.right.height + 1;
}
else if (node.right == null)
{
node.height = node.left.height + 1;
}
else
{
node.height = 1 + max(node.left.height, node.right.height);
}
}
private int max(int height, int height2) {
if (height > height2)
{
return height;
}
else
{
return height2;
}
}
public int height()
{
return root.height + 1;
}
Then I will call the updateHeight(Node node) method with the root as the parameter. However, it's not working when I test it this way:
public static void main(String[] arg)
{
BST bst = new BST();
bst.add("a");
bst.add("b");
bst.add("c");
System.out.println(bst.height());
bst.remove("c");
System.out.println(bst.height());
}
It's returning 2, then 2.
Just in case, here is my add method:
public boolean add(E e) throws NullPointerException
{
if (e == null)
{
throw new NullPointerException("Error: Cannot add a null object to the tree.");
}
if (root == null)
{
root = new Node(e);
return true;
}
Node current = root;
while (current != null ) {
if (current.data.compareTo(e) > 0) {
//add in the left subtree
if (current.left == null ) {
current.left = new Node (e);
size++;
this.updateHeight(root);
return true;
}
else {
current = current.left;
}
}
else if (current.data.compareTo(e) < 0) {
//add in the right subtree
if (current.right == null ) {
size++;
this.updateHeight(root);
current.right = new Node(e);
return true;
}
else {
current = current.right;
}
}
else { //duplicate
return false;
}
}
//should never get to this line
return false;
}

Binary Tree Traversal not showing full list

so currently I’m trying to follow a tutorial from FreeCodeCamp on implementing a Binary tree, but I’m having trouble with adding to and traversing through my tree.
For some reason, it seems that I’m able to add nodes to my tree, but when I try to traverse through my tree via iterative preorder traversal, it only picks up my root node. Its as if my nodes aren’t pointing to each other.
I have a feeling that the problem either lies with my add method or my traversal method, both of which are below. Any help would be greatly appreciated.
Add method:
public boolean add(T thing)
{
if(contains(thing))
{
return false;
} else {
root = add(root,thing);
count++;
return true;
}
}
private Node add(Node node,T thing)
{
if(node == null)
{
node = new Node(thing,null,null);
} else
{
if(thing.compareTo(node.value) <0)
{
if(node.left == null)
{
node.left = node = new Node(thing,null,null);
} else{
node.left =add(node.left,thing);
}
}
else
{
if(node.right == null)
{
node.right = node = new Node(thing,null,null);
}else {
node.right = add(node.right,thing);
}
}
}
return node;
}
Traversal:
public void traverse()
{
preorder(root);
}
private void preorder(Node node)
{ int iteration=0;
java.util.Stack<Node> stack = new java.util.Stack<Node>();
System.out.println( "root is: " +node.value);
stack.push(node);
while(stack.empty() == false)
{
Node current = stack.pop();
System.out.println("in preorder: "+current.value);
if(current.right != null)
{
stack.push(current.right);
}
if(current.left != null)
{
stack.push(current.left);
}
iteration++;
}
System.out.println("iteration: "+iteration);
}

You are not traversing your tree while adding in the tree. Check my tree insert method to get the idea:-
void insert(Node temp,int value) {
if(temp==null){
temp=new Node(value,null,null);
this.root=temp;
}
else{
Queue<Node> q = new LinkedList<>();
q.add(temp);
while (!q.isEmpty()) {
temp = q.peek();
q.remove();
if (temp.left == null) {
temp.left = new Node(value, null, null);
break;
} else
q.add(temp.left);
if (temp.right == null) {
temp.right =new Node(value, null, null);
break;
} else
q.add(temp.right);
}
}
}

Generic BST not inserting all values and returning null

I'm trying to implement a generic binary search tree. I'm inserting 7 integers and want them to return with inOrder traversal however it's only returning 4 values out of order. Then I check if the tree contains a specific value but it always returns null and i'm unsure why. I'll post the code below, any idea's on why my output is what it is? I know my issues are probably within my insert and find methods, but unsure why, some clarification would be nice. Appreciate any advice, thanks!
Output when inserting integers 15, 10, 20, 5, 13, 11, 19:
run:
InOrder:
Inorder traversal: 10 15 11 19
Is 11 in the tree? null
BUILD SUCCESSFUL (total time: 0 seconds)
Node.class:
class Node<E> {
protected E element;
protected Node<E> left;
protected Node<E> right;
public Node(E e) {
element = e;
}
}
BinarySearchTree.class:
class BinarySearchTree<E extends Comparable<E>> {
private Node<E> root;
public BinarySearchTree() {
root = null;
}
public Node find(E e) {
Node<E> current = root;
while (e.compareTo(current.element) != 0) {
if (e.compareTo(current.element) < 0) {
current = current.left;
}
else {
current = current.right;
}
if (current == null) {
return null;
}
}
return current;
}
public void insert(E e) {
Node<E> newNode = new Node<>(e);
if (root == null) {
root = newNode;
} else {
Node<E> current = root;
Node<E> parent = null;
while (true) {
parent = current;
if (e.compareTo(current.element) < 0) {
current = current.left;
}
if (current == null) {
parent.left = newNode;
return;
} else {
current = current.right;
if (current == null) {
parent.right = newNode;
return;
}
}
}
}
}
public void traverse(int traverseType) {
switch(traverseType) {
case 1: System.out.print("\nPreorder traversal: ");
preOrder(root);
break;
case 2: System.out.print("\nInorder traversal: ");
inOrder(root);
break;
case 3: System.out.print("\nPostorder traversal: ");
postOrder(root);
break;
}
System.out.println();
}
private void inOrder(Node<E> localRoot) {
if (localRoot != null) {
inOrder(localRoot.left);
System.out.print(localRoot.element + " ");
inOrder(localRoot.right);
}
}
private void preOrder(Node<E> localRoot) {
if (localRoot != null) {
System.out.print(localRoot.element + " ");
preOrder(localRoot.left);
preOrder(localRoot.right);
}
}
private void postOrder(Node<E> localRoot) {
if (localRoot != null) {
postOrder(localRoot.left);
postOrder(localRoot.right);
System.out.print(localRoot.element + " ");
}
}
}
Main class:
public class BST_Test{
public static void main(String[] args) {
testInteger();
}
static void testInteger() {
BinarySearchTree<Integer> itree = new BinarySearchTree<>();
itree.insert(15);
itree.insert(10);
itree.insert(20);
itree.insert(5);
itree.insert(13);
itree.insert(11);
itree.insert(19);
// Traverse tree
System.out.print("InOrder: ");
itree.traverse(2);
// Search for an element
System.out.println("Is 11 in the tree? " + itree.find(11));
}
}

The cause is your poorly formatted code is hiding the fact your insert method is incorrect.
This if statement does not have an opening curly brace { (and subsequently the closing curly brace } since it compiles), so as a result only the subsequent statement is included in this if block:
if (e.compareTo(current.element) < 0)
current = current.left
This means the following is executed regardless of whether the condition above is true...
if (current == null) {
parent.left = newNode;
return;
} ...
... and as a result if current != null, your insertion will then proceed to the right:
... else {
current = current.right;
if (current == null) {
parent.right = newNode;
return;
}
}
In full your current erroneous code, when formatted/indented appropriately is:
public void insert(E e) {
Node<E> newNode = new Node<>(e);
if (root == null) {
root = newNode;
} else {
Node<E> current = root;
Node<E> parent = null;
while (true) {
parent = current;
if (e.compareTo(current.element) < 0) // missing { ...
current = current.left; // ... so only this is in the if block
if (current == null) {
parent.left = newNode;
return;
} else { // oops, this should be else to the e.compareTo(current.element) < 0 condition
current = current.right;
if (current == null) {
parent.right = newNode;
return;
}
}
}
}
}
Fixed code (assuming duplicates are allowed):
public void insert(E e) {
Node<E> newNode = new Node<>(e);
if (root == null) {
root = newNode;
} else {
Node<E> current = root;
Node<E> parent = null;
while (true) {
parent = current;
if (e.compareTo(current.element) < 0) {
current = current.left;
if (current == null) {
parent.left = newNode;
return;
}
} else {
current = current.right;
if (current == null) {
parent.right = newNode;
return;
}
}
}
}
}
Moral of the story: Keeping your code well-formatted and using curly braces for blocks will save you headaches.

Implementing nodeCount() and leafCount() in a binary search tree - java

I am trying to implement leafCount() and nodeCount() to this recursive binary tree - program.
When testing it, these two methods (or the tests of them) throw AssertionError, so obviously they're not working as expected. I cannot figure out where I'm doing or thinking wrong. If someone could explain what I'm doing wrong or pinpoint the problem, I would be very grateful.
public class BSTrec {
BSTNode tree, parent, curr;
public BSTrec () {
tree = null; // the root of the tree
parent = null; // keeps track of the parent of the current node
curr = null; // help pointer to find a node or its place in the tree
}
public boolean isEmpty() {
return tree == null;
}
private boolean findNodeRec(String searchKey, BSTNode subtree, BSTNode subparent) {
if (subtree == null) { // base case 1: node not found
curr = null;
parent = subparent; // the logical parent for the value
return false;
}
else {
if (subtree.info.key.equals(searchKey)) {
curr = subtree; // update current to point to the node
parent = subparent; // update parent to point to its parent
return true;
}
else {
if (searchKey.compareTo(subtree.info.key) < 0) {
return findNodeRec(searchKey, subtree.left, subtree);
}
else {
return findNodeRec(searchKey, subtree.right, subtree);
}
}
}
}
public NodeInfo retrieveNode(String searchKey) {
if (findNodeRec(searchKey, tree, null)) return curr.info;
else return null;
}
public void addRec(String keyIn, BSTNode subtree, BSTNode subparent, boolean goLeft) {
if (tree == null) { // a first node will be the new root: base case 1
tree = new BSTNode(new NodeInfo(keyIn));
curr = tree;
parent = null;
}
else { // insertion in an existing tree
if (subtree == null) {
if (goLeft) {
subparent.left = new BSTNode(new NodeInfo(keyIn));
curr = subparent.left;
parent = subparent;
}
else { // the new node is to be a left child
subparent.right = new BSTNode(new NodeInfo(keyIn));
curr = subparent.right;
parent = subparent;
}
}
else {
if (keyIn.compareTo(subtree.info.key) < 0) {
addRec(keyIn, subtree.left, subtree, true);
}
else {
addRec(keyIn, subtree.right, subtree, false);
}
}
}
}
public void deleteNode(String searchKey) {
boolean found = findNodeRec(searchKey, tree, null);
if (!found) // the key is not in the tree
System.out.println("The key is not in the tree!");
else {
if ((curr.left == null) && (curr.right == null))
if (parent == null)
tree = null;
else
if (curr == parent.left) // delete a left child
parent.left = null;
else // delete a right child
parent.right = null;
else // delete a node with children, one or two
if ((curr.left != null) && (curr.right != null)) { // two children
BSTNode surrogateParent = curr;
BSTNode replacement = curr.left;
while (replacement.right != null) {
surrogateParent = replacement;
replacement = replacement.right;
}
curr.info = replacement.info; // the information is copied over
if (curr == surrogateParent) {
curr.left = replacement.left; // curr "adopts" the left
replacement = null;
}
else {
surrogateParent.right = replacement.left;
replacement = null;
}
} // End: if two children
else { // delete a node with one child
if (parent == null)
if (curr.left != null)
tree = curr.left;
else
tree = curr.right;
else
if (curr == parent.left)
if (curr.right == null)
parent.left = curr.left;
else
parent.left = curr.right;
else
if (curr.right == null)
parent.right = curr.left;
else
parent.right = curr.right;
}
curr = null;
}
}
public void inOrder(BSTNode root) {
if (root != null) {
inOrder(root.left); // process the left subtree
System.out.println(root.info.key); // process the node itself
inOrder(root.right); // process the right subtree
}
}
public void preOrder(BSTNode root) {
if (root != null) { // implicit base case: empty tree: do nothing
System.out.println(root.info.key); // process the node itself
preOrder(root.left); // process the left subtree
preOrder(root.right); // process the right subtree
}
}
public void postOrder(BSTNode root) {
if (root != null) { // implicit base case: empty tree: do nothing
postOrder(root.left); // process the left subtree
postOrder(root.right); // process the right subtree
System.out.println(root.info.key); // process the node itself
}
}
public int nodeCount() {
int count = 0;
if (tree == null) {
count = 0;
//throw new NullPointerException();
}
else {
if (tree.left != null) {
count = 1;
count += tree.left.nodeCount();
}
if (tree.right != null) {
count = 1;
count += tree.right.nodeCount();
}
}
return count;
}
public int leafCount() {
int count = 0;
if (tree == null) {
return 0;
}
if (tree != null && tree.left == null && tree.right==null) {
return 1;
}
else {
count += tree.left.leafCount();
count += tree.right.leafCount();
}
return count;
}
private class BSTNode {
NodeInfo info;
BSTNode left, right;
BSTNode() {
info = null;
left = null;
right = null;
}
public int leafCount() {
// TODO Auto-generated method stub
return 0;
}
public int nodeCount() {
// TODO Auto-generated method stub
return 0;
}
BSTNode(NodeInfo dataIn) {
info = dataIn;
left = null;
right = null;
}
BSTNode(NodeInfo dataIn, BSTNode l, BSTNode r) {
info = dataIn;
left = l;
right = r;
}
}
}
public class NodeInfo {
String key; // add other fields as needed!
NodeInfo() {
key = null;
}
NodeInfo(String keyIn) {
key = keyIn;
}
}

Your nodeCount logic has an error :
if (tree.left != null) {
count = 1;
count += tree.left.nodeCount();
}
if (tree.right != null) {
count = 1; // here you initialize the count, losing the count of the left sub-tree
count += tree.right.nodeCount();
}
Change to
if (tree.left != null || tree.right != null) {
count = 1;
if (tree.left != null) {
count += tree.left.nodeCount();
}
if (tree.right != null) {
count += tree.right.nodeCount();
}
}
In your leafCount you are missing some null checks, since it's possible one of the children is null :
if (tree != null && tree.left == null && tree.right==null) {
return 1;
} else {
if (tree.left != null) // added check
count += tree.left.leafCount();
if (tree.right != null) // added check
count += tree.right.leafCount();
}

In here:
public int leafCount() {
int count = 0;
if (tree == null) {
return 0;
}
if (tree != null && tree.left == null && tree.right==null) {
return 1;
}
else {
count += tree.left.leafCount();
count += tree.right.leafCount();
}
return count;
}
you're not allowing for the possibility that tree.left is non-null but tree.right is null. In that case, you'll try to execute
count += tree.right.leafCount();
which will throw a NullPointerException.
I think you should also rethink what you're doing with your instance fields curr and parent. These really should be local variables in whatever method you need to use them in. A tree doesn't have a "current" node in any meaningful sense.

Pairwise swap elements of a given linked list (Java solution)

I want to solve the following task:
Given a singly linked list, write a function to swap elements
pairwise. For example, if the linked list is 1->2->3->4->5->6->7 then
the function should change it to 2->1->4->3->6->5->7, and if the
linked list is 1->2->3->4->5->6 then the function should change it to
2->1->4->3->6->5
To do so, I use recursive approach taken from here: http://www.geeksforgeeks.org/pairwise-swap-elements-of-a-given-linked-list-by-changing-links/ , namely, swap the first two nodes, and then recurse on the rest of the list. My function is the following:
private static ListNode reorder(ListNode l1) {
if(l1 == null || l1.next == null)
return l1;
ListNode rest = l1.next.next;
//change head
ListNode newHead = l1.next;
//change next of second node
newHead.next = l1;
l1.next = reorder(rest);
return newHead;
}
However on the input 1 2 3 4 5 6 I have output 1 4 3 6 5?! I debugged it but still can't see where is the problem. Can anyone explain me why this is the case? Here is the whole class:
public class Swap {
public static class ListNode {
int val;
ListNode next;
ListNode(int x) {
val = x;
next = null;
}
}
public static void main(String[] args) {
ListNode l1 = new ListNode(1);
ListNode l2 = new ListNode(2);
ListNode l3 = new ListNode(3);
ListNode l4 = new ListNode(4);
ListNode l5 = new ListNode(5);
ListNode l6 = new ListNode(6);
ListNode l7 = new ListNode(7);
ListNode l8 = new ListNode(8);
ListNode l9 = new ListNode(9);
ListNode l10 = new ListNode(10);
l1.next = l2;
l2.next = l3;
l3.next = l4;
l4.next = l5;
l5.next = l6;
l7.next = l8;
l9.next = l10;
print(l1);
reorder(l1);
System.out.println();
print(l1);
}
private static void print(ListNode l1) {
ListNode current = l1;
while(current != null){
System.out.print(current.val + " ");
current = current.next;
}
}
private static ListNode reorder(ListNode l1) {
if(l1 == null || l1.next == null)
return l1;
ListNode rest = l1.next.next;
//change head
ListNode newHead = l1.next;
//change next of second node
newHead.next = l1;
l1.next = reorder(rest);
return newHead;
}
}

You're printing the list starting at l1, which is now the second element. You want to call
print(reorder(l1));

This is a recursive approach I did, it works for me. Let me know if there is any problem.
public void pairwiseSwap(Node node){
if(size() == 0){
System.out.println("empty");
return;
}
if(node.next == null){
System.out.println(node.value);
return;
}
Node one = node;
Node two = node.next;
System.out.println(two.value);
System.out.println(one.value);
if(two.next == null)
return;
pairwiseSwap(two.next);
}

your list is not well connected, you are missing these links:
l6.next = l7;
l8.next = l9;

Here is the solution for most f the linked list replated problems
Insert at Start
Insert at End
Insert at Position
Get the size of the list
Display the list
Delete from the list
Replace the node
Search item position in the list
Find the middle of the list"
Get the item from the last
Reverse the list
Swap the node of the list
Pairwise swap the list
Make the last node as the first node
Node.java
package com.practice.ds.list;
final public class Node<T> {
public Node<T> next = null;
public Node<T> prev = null;
public T data = null;
public Node() {
}
public Node(T data) {
this.data = data;
}
#Override
public String toString() {
return "Node [next=" + next + ", prev=" + prev + ", data=" + data + "]";
}
}
LinkedList.java
package com.practice.ds.list;
public class LinkedList<T> {
private Node<T> head = null;
private Node<T> tail = null;
public void insertAtStart(T data) {
throwEmptyDataException(data);
Node<T> node = new Node<T>(data);
if(empty()) {
head = node;
tail = head;
}else {
node.next = head;
head = node;
}
display();
}
public void insertAtEnd(T data) {
throwEmptyDataException(data);
if(empty()) {
insertAtStart(data);
}else {
Node<T> node = new Node<T>(data);
tail.next = node;
tail = node;
display();
}
}
public void insertAtPosition(int position, T data) {
throwEmptyDataException(data);
if (position < 1 || position > size() || empty())
throw new IllegalArgumentException("Can't perform insertion. Please check your inputs");
Node<T> node = head;
Node<T> tempNode = node;
for (int i = 1; i <= size(); i++) {
if (i == position) {
if (node == head) {
insertAtStart(data);
return;
} else {
Node<T> newNode = new Node<T>(data);
tempNode.next = newNode;
newNode.next = node;
display();
break;
}
}
tempNode = node;
node = node.next;
}
}
public boolean delete(int position) {
if (empty() || position < 1 || position > size())
return false;
Node<T> node = head;
Node<T> tempNode = node;
for (int i = 1; i <= size(); i++) {
if(i == position) {
if(node == head) {
head = head.next;
return true;
}else if(node == tail) {
tempNode.next = null;
tail = tempNode;
return true;
}else {
tempNode.next = node.next;
return true;
}
}
tempNode = node;
node = node.next;
}
return false;
}
public T replace(int position, T data) {
throwEmptyDataException(data);
if (empty() || position < 1 || position > size())
return null;
Node<T> node = head;
for (int i = 1; i <= size(); i++) {
if(i == position) {
T replaceData = node.data;
node.data = data;
return replaceData;
}
node = node.next;
}
return null;
}
public boolean search(T data) {
Node<T> node = head;
while(node != null && !node.data.equals(data)) {
node = node.next;
}
return node != null;
}
public T middle() {
Node<T> slowPtr = head;
Node<T> fastPtr = head;
while(fastPtr != null && fastPtr.next != null) {
slowPtr = slowPtr.next;
fastPtr = fastPtr.next.next;
}
return empty() ? null : slowPtr.data;
}
public T getElementFromLast(int position) {
if(empty() || position < 1 || position > getSizeIteratively())
return null;
Node<T> firstPtr = head;
Node<T> secondPtr = head;
for(int i = 1;i<=size();i++) {
if(i > position)
firstPtr = firstPtr.next;
if(secondPtr.next == null)
return firstPtr.data;
secondPtr = secondPtr.next;
}
return null;
}
public void reverse() {
Node<T> prev = null;
Node<T> current = head;
Node<T> next = null;
while(current != null) {
next = current.next;
current.next = prev;
prev = current;
current = next;
}
swapHeadTail();
displayIteratively();
}
public void reverseRecursively() {
reverseRecursively(head);
swapHeadTail();
display();
}
private Node<T> reverseRecursively(Node<T> node) {
if(node == null || node.next == null)
return node;
Node<T> secondNode = node.next;
node.next = null;
Node<T> reverseRest = reverseRecursively(secondNode);
secondNode.next = node;
return reverseRest;
}
private void swapHeadTail() {
Node<T> temp = head;
head = tail;
tail = temp;
}
public void swapPairwise() {
if(empty())
return;
Node<T> firstNode = head;
Node<T> secondNode = firstNode.next;
while(firstNode != null && secondNode != null) {
swap(firstNode.data, secondNode.data);
firstNode = firstNode.next;
if(firstNode != null)
secondNode = firstNode.next;
}
}
public void swap(T firstData, T secondData) {
throwEmptyException();
throwEmptyDataException(firstData);
throwEmptyDataException(secondData);
if(firstData.equals(secondData))
throw new IllegalArgumentException(firstData +" & "+ secondData+" both are the same. Can't swap");
Node<T> firstDataPtr = head;
Node<T> prevfirstDataPtr = firstDataPtr;
while (firstDataPtr != null && !firstDataPtr.data.equals(firstData)) {
prevfirstDataPtr = firstDataPtr;
firstDataPtr = firstDataPtr.next;
}
Node<T> secondDataPtr = head;
Node<T> prevSecondDataPtr = secondDataPtr;
while (secondDataPtr!= null && !secondDataPtr.data.equals(secondData)) {
prevSecondDataPtr = secondDataPtr;
secondDataPtr = secondDataPtr.next;
}
if(!(firstDataPtr == null || secondDataPtr == null)) {
// either first node or second node is head node
if (firstDataPtr == head)
head = secondDataPtr;
else if (secondDataPtr == head)
head = firstDataPtr;
// either first node or second node is tail node
if (firstDataPtr == tail)
tail = secondDataPtr;
else if (secondDataPtr == tail)
tail = firstDataPtr;
// getting the next pointer of both nodes
Node<T> nextFirstDataPtr = firstDataPtr.next;
Node<T> nextSecondDataPtr = secondDataPtr.next;
// swapping the nodes
prevfirstDataPtr.next = secondDataPtr;
secondDataPtr.next = nextFirstDataPtr;
prevSecondDataPtr.next = firstDataPtr;
firstDataPtr.next = nextSecondDataPtr;
// checking if both node is adjacent node
// if both nodes are adjacent re-adjust the pointer
if(nextFirstDataPtr == secondDataPtr) {
secondDataPtr.next = firstDataPtr;
} else if(nextSecondDataPtr == firstDataPtr) {
firstDataPtr.next = secondDataPtr;
}
} else
throw new IllegalArgumentException("Either "+firstData+" or "+secondData+" not present in the list");
displayIteratively();
}
public void setLastNodeAsFirstNode() {
if(empty() || head.next == null) {
return;
}
Node<T> node = head;
Node<T> prevNode = node;
while (node.next != null) {
prevNode = node;
node = node.next;
}
node.next = head;
head = node;
prevNode.next = null;
tail = prevNode;
display();
}
public int getSizeIteratively() {
if (empty())
return 0;
int size = 0;
Node<T> node = head;
while (node != null) {
++size;
node = node.next;
}
return size;
}
public int size() {
return size(head, 0);
}
private int size(Node<T> node, int size) {
return node != null ? size(node.next, ++size) : size;
}
public void displayIteratively() {
Node<T> node = head;
while (node != null) {
System.out.print(node.data + " ");
node = node.next;
}
}
public void display() {
display(head);
}
private void display(Node<T> node) {
if (node != null) {
System.out.print(node.data + " ");
display(node.next);
}
}
public void throwEmptyException() {
if (empty())
throw new IllegalArgumentException("List is empty!");
}
private void throwEmptyDataException(T data) {
if (data == null)
throw new IllegalArgumentException("data is null !");
}
public boolean empty() {
return head == null;
}
}
LinkedListTest.java
package com.practice.ds.list;
import java.util.Scanner;
public class LinkedListTest {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
LinkedList<Integer> list = new LinkedList<>();
boolean exit = false;
do {
System.out.println("\n----------------------------------------");
System.out.println("1. Insert at Start");
System.out.println("2. Insert at End");
System.out.println("3. Insert at Position");
System.out.println("4. Get the size of list");
System.out.println("5. Display the list");
System.out.println("6. Delete from the list ");
System.out.println("7. Replace the node ");
System.out.println("8. Search item position in the list ");
System.out.println("9. Find the middle of the list");
System.out.println("10. Get item from the last : ");
System.out.println("11. Reverse the list :: ");
System.out.println("12. Swap the node of the list");
System.out.println("13. Pairwise swap the list");
System.out.println("14. Make last node as first node");
System.out.println("15. Segregate even and odd node");
System.out.println();
int choice = scanner.nextInt();
switch (choice) {
case 1:
try {
System.out.println("Insert the node : ");
int node = scanner.nextInt();
list.insertAtStart(node);
} catch (Exception e) {
e.printStackTrace();
}
break;
case 2:
try {
System.out.println("Insert the node : ");
int node = scanner.nextInt();
list.insertAtEnd(node);
} catch (Exception e) {
e.printStackTrace();
}
break;
case 3:
try {
System.out.println("Enter the position :");
int position = scanner.nextInt();
System.out.println("Insert the node :");
int node = scanner.nextInt();
list.insertAtPosition(position, node);
} catch (Exception e) {
e.printStackTrace();
}
break;
case 4:
try {
System.out.println("Getting the size :: ");
System.out.println("1. Get Iteratively");
System.out.println("2. Get Recursively");
int input = scanner.nextInt();
switch (input) {
case 1:
System.out.println("The size of the list :: " + list.getSizeIteratively());
break;
case 2:
System.out.println("The size of the list :: " + list.size());
break;
default:
System.out.println("Invalid input...!");
break;
}
} catch (Exception e) {
e.printStackTrace();
}
break;
case 5:
try {
System.out.println("Displaying the list :: ");
System.out.println("1. Display Iteratively");
System.out.println("2. Display Recursively");
int input = scanner.nextInt();
switch (input) {
case 1:
list.displayIteratively();
break;
case 2:
list.display();
break;
default:
System.out.println("Invalid input...!");
break;
}
} catch (Exception e) {
e.printStackTrace();
}
break;
case 6:
try {
System.out.println("Enter the position ");
int position = scanner.nextInt();
System.out.println("is Delete :: " + list.delete(position));
} catch (Exception e) {
e.printStackTrace();
}
break;
case 7:
try {
System.out.println("Enter the position ");
int position = scanner.nextInt();
System.out.println("Insert the item ");
int data = scanner.nextInt();
list.replace(position, data);
} catch (Exception e) {
e.printStackTrace();
}
break;
case 8:
try {
System.out.println("Note: It will give first occurence of the item ");
System.out.println("Enter the item ");
int data = scanner.nextInt();
System.out.println(list.search(data));
} catch (Exception e) {
e.printStackTrace();
}
break;
case 9:
try {
System.out.println("The Middle node of the list is :: " + list.middle());
} catch (Exception e) {
e.printStackTrace();
}
break;
case 10:
System.out.println("Enter the position ");
try {
int position = scanner.nextInt();
System.out.println("Element is :: " + list.getElementFromLast(position));
} catch (Exception e) {
e.printStackTrace();
}
break;
case 11:
System.out.println("Reversing the list...");
System.out.println("1. Iteratively");
System.out.println("2. Recursively");
int key = scanner.nextInt();
switch (key) {
case 1:
try {
list.reverse();
} catch (Exception e) {
e.printStackTrace();
}
break;
case 2:
try {
list.reverseRecursively();
} catch (Exception e) {
e.printStackTrace();
}
break;
default:
System.out.println("Your choice is out of the box...! \ntry again...");
break;
}
break;
case 12:
try {
System.out.println("Enter first node ");
int firstNode = scanner.nextInt();
System.out.println("Enter second node ");
int secondNode = scanner.nextInt();
list.swap(firstNode, secondNode);
} catch (Exception e) {
e.printStackTrace();
}
break;
case 13:
try {
list.swapPairwise();
} catch (Exception e) {
e.printStackTrace();
}
break;
case 14:
try {
list.setLastNodeAsFirstNode();
} catch (Exception e) {
e.printStackTrace();
}
break;
default:
System.out.println("Your choice is out of the box...! \ntry again...");
break;
}
} while (!exit);
scanner.close();
}
}