Java linkedlist implementation overwriting node

Question

I wanted to learn about linked list, so I tried to implement one from scratch. The logic makes sense, however when adding a value to the linkedlist it overwrites the values. So if I added the ones 1 -> 2 -> 3 -> 4 -> 5, but I wont get these values when I print the content of my linked list...

Any idea how to fix the solution?

public class LinkedListM {
    Node head;

    class Node {
        Node next;
        int value;

        Node(int value) {
            this.value = value;
            this.next = null;
        }
    }
    
    public void add(int value) {
        // System.out.println("inserting: " + value);
        Node node = new Node(value);
        if (head == null) {
            head = node;
        }
        else {
            while (head.next != null) {
                // System.out.println(head.value + " -> " + head.next.value);
                head = head.next;
            }
            head.next = node;
        }
    }

    public void remove(int value) {
        LinkedListM list = new LinkedListM();
        Node dummy = new Node(0);
        dummy.next = head;

        while (dummy.next != null) {
            if (dummy.next.value == value) {
                if (dummy.next.next == null) {
                    dummy.next = null;
                }
                else {
                    dummy.next = dummy.next.next;
                }
            }
            dummy = dummy.next;
        }
    }
}

Here is me testing the linked list:


public class p {
    
    public static void main(String[] args) {
        LinkedListM ll = new LinkedListM();
        ll.add(1);
        ll.add(2);
        ll.add(3);
        ll.add(4);
        ll.add(5);

        // System.out.println(ll);

        while(ll.head.next != null) {
            System.out.print(ll.head.value + " -> ");
            ll.head = ll.head.next;
        }
        System.out.println();
    }
}

In the case where head != null you are modifying head. You need a local variable. — tgdavies
– tgdavies, Commented Oct 2, 2022 at 3:43

abdo Salm · Accepted Answer · 2022-10-02 03:54:48Z

first of all, writing ll.head = ll.head.next; is a bad practice because you are changing the head of the linked list, instead create a dummy Node and use it to iterate all over the array, so instead of :

while(ll.head.next != null) {
    System.out.print(ll.head.value + " -> ");
    ll.head = ll.head.next;
}
System.out.println();

you should write:

LinkedListM.Node dummy = ll.head;
while(dummy != null) {
    System.out.print(dummy.value + " -> ");
    dummy = dummy.next;
}
System.out.println();

again, in the code of inserting nodes, you are writing:

head = head.next;

which will change the head of the linked list, instead create a dummy node and use it to insert into the linked list or make a tail Node for the linked list like:

tail.next = node;
tail = node;

instead of

while (head.next != null) {
    // System.out.println(head.value + " -> " + head.next.value);
    head = head.next;
}
head.next = node;

apply the same concept for your function called remove as it has some logical errors.

this is the code edited:

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
import java.util.regex.Pattern;

public class Main {

    public static void main(String[] args) {
        LinkedListM ll = new LinkedListM();
        ll.add(1);
        ll.add(2);
        ll.add(3);
        ll.add(4);
        ll.add(5);



        // System.out.println(ll);
        LinkedListM.Node dummy = ll.head;
        while(dummy != null) {
            System.out.print(dummy.value + " -> ");
            dummy = dummy.next;
        }
        System.out.println();

        System.out.println("removing value 3");
        ll.remove(3);

        dummy = ll.head;
        while(dummy != null) {
            System.out.print(dummy.value + " -> ");
            dummy = dummy.next;
        }
        System.out.println();

    }

}
 class LinkedListM {
    Node head;
    Node tail;

    class Node {
        Node next;
        int value;

        Node(int value) {
            this.value = value;
            this.next = null;
        }
    }

    public void add(int value) {
        // System.out.println("inserting: " + value);
        Node node = new Node(value);
        if (head == null) {
            head = node;
            tail = node;
        }
        else
        {
            tail.next = node;
            tail = node;
        }
    }

    public void remove(int value) {
        Node dummy = head;

        if (head.value == value)
        {
            head = head.next;
        }
        else
        {
            while (dummy.next != null && dummy.next.value != value)
                dummy = dummy.next;

            if (dummy.next != null)
                dummy.next = dummy.next.next;

        }
    }
}

and this is the output:

1 -> 2 -> 3 -> 4 -> 5 -> 
removing value 3
1 -> 2 -> 4 -> 5 ->

Collectives™ on Stack Overflow

Java linkedlist implementation overwriting node

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related