Description

To remove duplicate elements from singly linked list - 
Case 1: check if list is empty 
    Show message that list is empty.
Case 2: If list has elements 
    a) Take two loops
    b) Outer loop is used to pick the elements one by one
    c) inner loop compares the picked element with the rest of the elements.

Note: Here head contains the address of first node

C/C++

/* C Program to Remove Duplicate Elements In Singly Linked List */
//Save it as RemoveDuplicateElements.c

#include<stdio.h>
#include<malloc.h>
struct node *create(int);
void display(struct node *);

//Declaring node
struct node{
    int data;
    struct node *next;
};

int main(){
    int n, val;
    struct node *head;
    printf("Enter number of nodes : ");
    scanf("%d",&n);
    
    //Calling function to create node
    head=create(n);
    
    //Calling function to display list
    display(head);

    removeDuplicate(head);

    printf("\nList after removing duplicates: \n");
    display(head);

    return 0;
}

struct node *create(int n){
    int i;
    struct node *head=NULL;
    struct node *address,*newNode;

    for(i=0;i<n;i++){
        
        //Creating a new node
        newNode=(struct node*)malloc(sizeof(struct node*));
        
        //Assigning data to newly created node
        printf("Enter the value of %d node : ",i+1);
        scanf("%d",&newNode->data);
        newNode->next=NULL;
        
        /*If list is empty assign the address of newly created node to head*/
        if(head==NULL){
            head=newNode;
        }else{
            
            /* If list already have few elements then loop through
            list and add newly created node after given node*/
            address=head;
            while(address->next!=NULL){
                address=address->next;
            }
            address->next=newNode;
        }
    }
    return head;
}

void display(struct node *head){
    struct node *address;
    
    //If list is empty
    if(head==NULL){
        printf("The linked list is empty");
    }else{
        
        /*If list has elements then loop through the loop and
        print elements one by one in sequential manner*/
        address=head;
        while(address!=NULL){
            printf("The node value = %d and their address = %u\n",address->data,address);
            address=address->next;
        }
    }
}

void removeDuplicate(struct node *head) {

    struct node *current = head, *index = NULL, *temp = NULL;

    if(head == NULL) {
        return;
    }
    else {
        while(current != NULL){
            temp = current;
            index = current->next;
            while(index != NULL) {
                if(current->data == index->data) {
                    temp->next = index->next;
                }
                else {
                    temp = index;
                }
                index = index->next;
            }
            current = current->next;
        }
    }
}

Input:
Enter number of node you want to enter : 
5
Enter value of 1 node : 
2
Enter value of 2 node : 
3
Enter value of 3 node : 
3
Enter value of 4 node : 
4
Enter value of 5 node : 
2

Output:
The nodes of lists are : 
2 3 3 4 2 
List after removing duplicates: 
The nodes of lists are : 
2 3 4

Java

/* Java Program to Remove Duplicate Elements In Singly Linked List */
//Save it as RemoveDuplicateElements.java

import java.io.*;
import java.util.Scanner;

public class RemoveDuplicateElements {
    
    // Declaring node
    class Node {
        int data;
        Node next;

        public Node(int data) {
            this.data = data;
            
            // Assigning null value to the next field
            this.next = null;
        }
    }

    public static Node head = null;
    
    // Function to add node
    public void addNode(int data) {
        
        // Creating a new node
        Node newNode = new Node(data);
        
        /* If list is empty assign the address of newly created node to head */
        if (head == null) {
            head = newNode;
        } else {
            
            /*If list already have few elements then loop through 
            list and add newly created node at the end of list*/
            Node ptr = head;
            while (ptr.next != null) {
                ptr = ptr.next;
            }
            ptr.next = newNode;
        }
    }

    public void display() {
        Node ptr = head;
        
        // If list is empty
        if (ptr == null) {
            System.out.println("The list is empty");
            return;
        }
        System.out.println("The nodes of lists are : ");
        
        /*
         * If list has elements then loop through the loop and print elements one by one
         * in sequential manner
         */
        while (ptr != null) {
            System.out.print(ptr.data + " ");
            ptr = ptr.next;
        }
    }

    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);

        RemoveDuplicateElements list = new RemoveDuplicateElements();

        System.out.println("Enter number of node you want to enter : ");
        int n = scanner.nextInt();

        for (int i = 0; i < n; i++) {
            System.out.println("Enter value of " + (i + 1) + " node : ");
            int val = scanner.nextInt();
            list.addNode(val);
        }
        
        // Calling function to display list
        list.display();

        removeDuplicate();

        System.out.println("\nList after removing duplicates: ");
        list.display();
    }
    
    // Function for removing duplicate elements from singly linked list
    public static void removeDuplicate() {
        Node current = head, index = null, temp = null;

        if (head == null) {
            return;
        } else {
            while (current != null) {
                temp = current;
                index = current.next;

                while (index != null) {
                    if (current.data == index.data) {
                        temp.next = index.next;
                    } else {
                        temp = index;
                    }
                    index = index.next;
                }
                current = current.next;
            }
        }
    }
}

Input:
Enter number of node you want to enter : 
5
Enter value of 1 node : 
2
Enter value of 2 node : 
3
Enter value of 3 node : 
3
Enter value of 4 node : 
4
Enter value of 5 node : 
2

Output:
The nodes of lists are : 
2 3 3 4 2 
List after removing duplicates: 
The nodes of lists are : 
2 3 4

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