What is wrong in my code?

#1

import java.util.*;

class LinkedList {

private class Node {

	int data;
	Node next;

	Node(int data, Node next) {
		this.data = data;
		this.next = next;
	}
}

private Node head;
private Node tail;
private int size;

public LinkedList() {
	this.head = null;
	this.tail = null;
	this.size = 0;
}

public LinkedList(Node head, Node tail, int size) {
	this.head = head;
	this.tail = tail;
	this.size = size;
}

// O(1)
public int size() {
	return this.size;
}

// O(1)
public boolean isEmpty() {
	return this.size() == 0;
}

// O(1)
public int getFirst() throws Exception {
	if (this.isEmpty()) {
		throw new Exception("List is empty.");
	}

	return this.head.data;
}

// O(1)
public int getLast() throws Exception {
	if (this.isEmpty()) {
		throw new Exception("List is empty.");
	}

	return this.tail.data;
}

// O(N)
public int getAt(int idx) throws Exception {
	Node temp = this.getNodeAt(idx);
	return temp.data;
}

// O(N)
private Node getNodeAt(int idx) throws Exception {
	if (this.isEmpty()) {
		throw new Exception("List is empty");
	}

	if (idx < 0 || idx >= this.size()) {
		throw new Exception("Invalid arguments");
	}

	Node retVal = this.head;
	for (int i = 0; i < idx; i++) {
		retVal = retVal.next;
	}

	return retVal;
}

// O(1)
public void addFirst(int data) {
	Node node = new Node(data, this.head);

	if (this.size() == 0) {
		this.head = node;
		this.tail = node;
	} else {
		this.head = node;
	}

	this.size++;
}

// O(1)
public void addLast(int data) {
	Node node = new Node(data, null);

	if (this.size() == 0) {
		this.head = node;
		this.tail = node;
	} else {
		this.tail.next = node;
		this.tail = node;
	}

	this.size++;
}

// O(n)
public void addAt(int idx, int data) throws Exception {
	if (idx < 0 || idx > this.size()) {
		throw new Exception("Invalid arguments");
	}

	if (idx == 0) {
		this.addFirst(data);
	} else if (idx == this.size()) {
		this.addLast(data);
	} else {
		Node nm1 = this.getNodeAt(idx - 1);
		Node n = nm1.next;

		Node node = new Node(data, n);
		nm1.next = node;

		this.size++;
	}
}

// O(1)
public int removeFirst() throws Exception {
	if (this.isEmpty()) {
		throw new Exception("List is empty");
	}

	int retVal = this.head.data;

	if (this.size() == 1) {
		this.head = null;
		this.tail = null;
	} else {
		this.head = this.head.next;
	}

	this.size--;
	return retVal;
}

// O(n)
public int removeLast() throws Exception {
	if (this.isEmpty()) {
		throw new Exception("List is empty");
	}

	int retVal = this.tail.data;

	if (this.size() == 1) {
		this.head = null;
		this.tail = null;
	} else {
		Node sm2 = this.getNodeAt(this.size() - 2);
		sm2.next = null;
		this.tail = sm2;
	}

	this.size--;
	return retVal;
}

// O(n)
public int removeAt(int idx) throws Exception {
	if (this.isEmpty()) {
		throw new Exception("List is empty");
	}

	if (idx < 0 || idx >= this.size()) {
		throw new Exception("Invalid arguments");
	}

	if (idx == 0) {
		return this.removeFirst();
	} else if (idx == this.size() - 1) {
		return this.removeLast();
	} else {
		Node nm1 = this.getNodeAt(idx - 1);
		Node n = nm1.next;
		Node np1 = n.next;

		nm1.next = np1;
		this.size--;

		return n.data;
	}
}

// O(n)
public void display() {
	Node node = this.head;

	while (node != null) {
		System.out.print(node.data + " ");
		node = node.next;
	}

	//System.out.println("END");
}

public void reverse(int k)throws Exception {

int hi=k-1;
	int lo=0;
	while(lo<hi) {
	    Node first=getNodeAt(lo);
	    Node end=getNodeAt(hi);
	    int temp=first.data;
	    first.data=end.data;
	    end.data=temp;
	    
	    
	    lo=hi+1;
	    hi=hi+k;
		

	}

}

}
class Main{
public static void main(String[] args) throws Exception {

	Scanner scn = new Scanner(System.in);
	int N = scn.nextInt();
    int k = scn.nextInt();
	
	LinkedList list = new LinkedList();

	for (int i = 0; i < N; i++) {
		list.addLast(scn.nextInt());
	}

    list.reverse(k);
	list.display();

}
}

#2

why are u not replying???

#3

your reverse function is not correct

look at this fucntion below
you have to do like that

node* reverse(node* head, int k) {

    if(head==NULL)return NULL;
	node* curr=head;
	node* prev=NULL;
	node* nxt=curr->next;
	int cnt=0;
	while(cnt<k&&curr){
		curr->next=prev;
		prev=curr;
		curr=nxt;
		if(curr)nxt=curr->next;
		cnt++;
	}
	head->next=reverse(curr,k);
	return prev;

}

your approach is similar to this but there are some mistakes and dont handle corner cases
correct this and it ll pass all your test casess :slight_smile:

#4

maam i have done it in java but u are providing c++ code why??

#5

refer to this