# Program To Remove Duplicate Elements From A Singly Linked List

Program To Remove Duplicate Elements From A Singly Linked List on fibonacci, factorial, prime, armstrong, swap, reverse, search, sort, stack, queue, array, linkedlist, tree, graph etc.

## Program to remove duplicate elements from a singly linked list

### Explanation

In this program, we need to remove the duplicate nodes from the given singly linked list.

Original List:

List after removing duplicate nodes:

In the above list, node 2 is repeated thrice, and node 1 is repeated twice. Node current will point to head, and index will point to node next to current. Start traversing the list till a duplicate is found that is when current's data is equal to index's data. In the above example, the first duplicate will be found at position 4. Assign current to another node temp. Connect temp's next node with index's next node. Delete index which was pointing to duplicate node. This process will continue until all duplicates are removed.

### Algorithm

1. Create a class Node which has two attributes: data and next. Next is a pointer to the next node in the list.
2. Create another class RemoveDuplicate which has two attributes: head and tail.
1. Create a new node.
2. It first checks, whether the head is equal to null which means the list is empty.
3. If the list is empty, both head and tail will point to a newly added node.
4. If the list is not empty, the new node will be added to end of the list such that tail's next will point to a newly added node. This new node will become the new tail of the list.
4. removeDuplicate() will remove duplicate nodes from the list.
1. Define a new node current which will initially point to head.
2. Node temp will point to current and index will always point to node next to current.
3. Loop through the list till current points to null.
4. Check whether current?s data is equal to index's data that means index is duplicate of current.
5. Since index points to duplicate node so skip it by making node next to temp to will point to node next to index, i.e. temp.next = index.next.
5. display() will display the nodes present in the list:
1. Define a node current which will initially point to the head of the list.
2. Traverse through the list till current points to null.
3. Display each node by making current to point to node next to it in each iteration.

### Python

```#Represent a node of the singly linked list
class Node:
def __init__(self,data):
self.data = data;
self.next = None;

class RemoveDuplicate:
def __init__(self):
self.tail = None;

#Create a new node
newNode = Node(data);

#Checks if the list is empty
#If list is empty, both head and tail will point to new node
self.tail = newNode;
else:
#newNode will be added after tail such that tail's next will point to newNode
self.tail.next = newNode;
#newNode will become new tail of the list
self.tail = newNode;

#removeDuplicate() will remove duplicate nodes from the list
def removeDuplicate(self):
#Node current will point to head
index = None;
temp = None;

return;
else:
while(current != None):
#Node temp will point to previous node to index.
temp = current;
#Index will point to node next to current
index = current.next;

while(index != None):
#If current node's data is equal to index node's data
if(current.data == index.data):
#Here, index node is pointing to the node which is duplicate of current node
#Skips the duplicate node by pointing to next node
temp.next = index.next;
else:
#Temp will point to previous node of index.
temp = index;
index = index.next;
current = current.next;

#display() will display all the nodes present in the list
def display(self):
#Node current will point to head
print("List is empty");
return;
while(current != None):
#Prints each node by incrementing pointer
print(current.data);
current = current.next;

sList = RemoveDuplicate();

print("Originals list: ");
sList.display();

#Removes duplicate nodes
sList.removeDuplicate();

print("List after removing duplicates: ");
sList.display();
```

Output:

``` Originals list:
1 2 3 2 2 4 1
List after removing duplicates:
1 2 3 4
```

### C

```#include <stdio.h>

//Represent a node of the singly linked list
struct node{
int data;
struct node *next;
};

struct node *head, *tail = NULL;

//Create a new node
struct node *newNode = (struct node*)malloc(sizeof(struct node));
newNode->data = data;
newNode->next = NULL;

//Checks if the list is empty
//If list is empty, both head and tail will point to new node
tail = newNode;
}
else {
//newNode will be added after tail such that tail's next will point to newNode
tail->next = newNode;
//newNode will become new tail of the list
tail = newNode;
}
}

//removeDuplicate() will remove duplicate nodes from the list
void removeDuplicate() {
//Node current will point to head
struct node *current = head, *index = NULL, *temp = NULL;

return;
}
else {
while(current != NULL){
//Node temp will point to previous node to index.
temp = current;
//Index will point to node next to current
index = current->next;

while(index != NULL) {
//If current node's data is equal to index node's data
if(current->data == index->data) {
//Here, index node is pointing to the node which is duplicate of current node
//Skips the duplicate node by pointing to next node
temp->next = index->next;
}
else {
//Temp will point to previous node of index.
temp = index;
}
index = index->next;
}
current = current->next;
}
}
}

//display() will display all the nodes present in the list
void display() {
//Node current will point to head
printf("List is empty \n");
return;
}
while(current != NULL) {
//Prints each node by incrementing pointer
printf("%d ", current->data);
current = current->next;
}
printf("\n");
}

int main()
{

printf("Originals list: \n");
display();

//Removes duplicate nodes
removeDuplicate();

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

return 0;
}
```

Output:

```Originals list:
1 2 3 2 2 4 1
List after removing duplicates:
1 2 3 4
```

### JAVA

```public class RemoveDuplicate {

//Represent a node of the singly linked list
class Node{
int data;
Node next;

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

public Node tail = null;

//Create a new node
Node newNode = new Node(data);

//Checks if the list is empty
//If list is empty, both head and tail will point to new node
tail = newNode;
}
else {
//newNode will be added after tail such that tail's next will point to newNode
tail.next = newNode;
//newNode will become new tail of the list
tail = newNode;
}
}

//removeDuplicate() will remove duplicate nodes from the list
public void removeDuplicate() {
//Node current will point to head
Node current = head, index = null, temp = null;

return;
}
else {
while(current != null){
//Node temp will point to previous node to index.
temp = current;
//Index will point to node next to current
index = current.next;

while(index != null) {
//If current node's data is equal to index node's data
if(current.data == index.data) {
//Here, index node is pointing to the node which is duplicate of current node
//Skips the duplicate node by pointing to next node
temp.next = index.next;
}
else {
//Temp will point to previous node of index.
temp = index;
}
index = index.next;
}
current = current.next;
}
}
}

//display() will display all the nodes present in the list
public void display() {
//Node current will point to head
System.out.println("List is empty");
return;
}
while(current != null) {
//Prints each node by incrementing pointer
System.out.print(current.data + " ");
current = current.next;
}
System.out.println();
}

public static void main(String[] args) {

RemoveDuplicate sList = new RemoveDuplicate();

System.out.println("Originals list: ");
sList.display();

//Removes duplicate nodes
sList.removeDuplicate();

System.out.println("List after removing duplicates: ");
sList.display();
}
}
```

Output:

```Originals list:
1 2 3 2 2 4 1
List after removing duplicates:
1 2 3 4
```

### C#

```using System;

public class CreateList
{
//Represent a node of the singly linked list
public class Node<T>{
public T data;
public Node<T> next;

public Node(T value) {
data = value;
next = null;
}
}

public class RemoveDuplicate<T>{
public Node<T> tail = null;

//Create a new node
Node<T> newNode = new Node<T>(data);

//Checks if the list is empty
//If list is empty, both head and tail will point to new node
tail = newNode;
}
else {
//newNode will be added after tail such that tail's next will point to newNode
tail.next = newNode;
//newNode will become new tail of the list
tail = newNode;
}
}

//removeDuplicate() will remove duplicate nodes from the list
public void removeDuplicate() {
//Node current will point to head
Node<T> current = head, index = null, temp = null;

return;
}
else {
while(current != null){
//Node temp will point to previous node to index.
temp = current;
//Index will point to node next to current
index = current.next;

while(index != null) {
//If current node's data is equal to index node's data
if(current.data.Equals(index.data)) {
//Here, index node is pointing to the node which is duplicate of current node
//Skips the duplicate node by pointing to next node
temp.next = index.next;
}
else {
//Temp will point to previous node of index.
temp = index;
}
index = index.next;
}
current = current.next;
}
}
}

//display() will display all the nodes present in the list
public void display() {
//Node current will point to head
Console.WriteLine("List is empty");
return;
}
while(current != null) {
//Prints each node by incrementing pointer
Console.Write(current.data + " ");
current = current.next;
}
Console.WriteLine();
}
}

public static void Main()
{
RemoveDuplicate<int> sList = new RemoveDuplicate<int>();

Console.WriteLine("Originals list: ");
sList.display();

//Removes duplicate nodes
sList.removeDuplicate();

Console.WriteLine("List after removing duplicates: ");
sList.display();
}
}
```

Output:

```Originals list:
1 2 3 2 2 4 1
List after removing duplicates:
1 2 3 4
```

### PHP

```<!DOCTYPE html>
<html>
<body>
<?php
//Represent a node of singly linked list
class Node{
public \$data;
public \$next;

function __construct(\$data){
\$this->data = \$data;
\$this->next = NULL;
}
}
class RemoveDuplicate{
public \$tail;
function __construct(){
\$this->tail = NULL;
}

//Create a new node
\$newNode = new Node(\$data);

//Checks if the list is empty
//If list is empty, both head and tail will point to new node
\$this->tail = \$newNode;
}
else {
//newNode will be added after tail such that tail's next will point to newNode
\$this->tail->next = \$newNode;
//newNode will become new tail of the list
\$this->tail = \$newNode;
}
}

//removeDuplicate() will remove duplicate nodes from the list
function removeDuplicate() {
//Node current will point to head
\$index = null;
\$temp = null;

return;
}
else {
while(\$current != null){
//Node temp will point to previous node to index.
\$temp = \$current;
//Index will point to node next to current
\$index = \$current->next;

while(\$index != null) {
//If current node's data is equal to index node's data
if(\$current->data == \$index->data) {
//Here, index node is pointing to the node which is duplicate of current node
//Skips the duplicate node by pointing to next node
\$temp->next = \$index->next;
}
else {
//Temp will point to previous node of index.
\$temp = \$index;
}
\$index = \$index->next;
}
\$current = \$current->next;
}
}
}

//display() will display all the nodes present in the list
function display() {
//Node current will point to head

print("List is empty <br>");
return;
}
while(\$current != NULL) {
//Prints each node by incrementing pointer
print(\$current->data . " ");
\$current = \$current->next;
}
print("<br>");
}
}

\$sList = new RemoveDuplicate();

print("Originals list: <br>");
\$sList->display();

//Removes duplicate nodes
\$sList->removeDuplicate();

print("List after removing duplicates: <br>");
\$sList->display();
?>
</body>
</html>
```

Output:

``` Originals list:
1 2 3 2 2 4 1
List after removing duplicates:
1 2 3 4
```

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