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

Create a class Node which has two attributes: data and next. Next is a pointer to the next node in the list.
Create another class RemoveDuplicate which has two attributes: head and tail.
addNode() will add a new node to the list:
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.
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.
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.

Solution

Python

  #Represent a node of the singly linked list  class Node:      def __init__(self,data):          self.data = data;          self.next = None;            class RemoveDuplicate:      #Represent the head and tail of the singly linked list      def __init__(self):          self.head = None;          self.tail = None;                #addNode() will add a new node to the list      def addNode(self, data):          #Create a new node          newNode = Node(data);                    #Checks if the list is empty          if(self.head == None):              #If list is empty, both head and tail will point to new node              self.head = newNode;              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          current = self.head;          index = None;          temp = None;                    if(self.head == 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          current = self.head;          if(self.head == None):              print(“List is empty”);              return;          while(current != None):              #Prints each node by incrementing pointer              print(current.data);              current = current.next;               sList = RemoveDuplicate();            #Adds data to the list  sList.addNode(1);  sList.addNode(2);  sList.addNode(3);  sList.addNode(2);  sList.addNode(2);  sList.addNode(4);  sList.addNode(1);     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;  };         //Represent the head and tail of the singly linked list  struct node *head, *tail = NULL;     //addNode() will add a new node to the list  void addNode(int data) {      //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(head == NULL) {          //If list is empty, both head and tail will point to new node          head = newNode;          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;            if(head == 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      struct node *current = head;      if(head == NULL) {          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()  {      //Adds data to the list      addNode(1);      addNode(2);      addNode(3);      addNode(2);      addNode(2);      addNode(4);      addNode(1);            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;          }      }         //Represent the head and tail of the singly linked list      public Node head = null;      public Node tail = null;            //addNode() will add a new node to the list      public void addNode(int data) {          //Create a new node          Node newNode = new Node(data);                    //Checks if the list is empty          if(head == null) {              //If list is empty, both head and tail will point to new node              head = newNode;              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;                    if(head == 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          Node current = head;          if(head == null) {              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();                    //Adds data to the list          sList.addNode(1);          sList.addNode(2);          sList.addNode(3);          sList.addNode(2);          sList.addNode(2);          sList.addNode(4);          sList.addNode(1);                    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>{          //Represent the head and tail of the singly linked list          public Node<T> head = null;                        public Node<T> tail = null;                //addNode() will add a new node to the list          public void addNode(T data) {              //Create a new node              Node<T> newNode = new Node<T>(data);                 //Checks if the list is empty              if(head == null) {                  //If list is empty, both head and tail will point to new node                  head = newNode;                  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;                 if(head == 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              Node<T> current = head;              if(head == null) {                  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>();                    //Adds data to the list          sList.addNode(1);          sList.addNode(2);          sList.addNode(3);          sList.addNode(2);          sList.addNode(2);          sList.addNode(4);          sList.addNode(1);                    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{      //Represent the head and tail of the singly linked list      public $head;      public $tail;      function __construct(){          $this->head = NULL;          $this->tail = NULL;      }            //addNode() will add a new node to the list      function addNode($data) {          //Create a new node          $newNode = new Node($data);                    //Checks if the list is empty          if($this->head == NULL) {              //If list is empty, both head and tail will point to new node              $this->head = $newNode;              $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          $current = $this->head;          $index = null;          $temp = null;                    if($this->head == 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          $current = $this->head;                    if($this->head == NULL) {              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();            //Adds data to the list  $sList->addNode(1);  $sList->addNode(2);  $sList->addNode(3);  $sList->addNode(2);  $sList->addNode(2);  $sList->addNode(4);  $sList->addNode(1);     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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Program To Remove Duplicate Elements From A Singly Linked List