Program to Remove Duplicate Elements From a Doubly Linked List

Q. Program to remove duplicate elements from a doubly linked list.

Explanation

In this program, we will create a doubly linked list and remove the duplicate, if present, by traversing through the list.

Original List:

Program to remove duplicate elements from a doubly linked list

List after removing duplicates:

Program to remove duplicate elements from a doubly linked list

In above list, node2 is repeated thrice, and node 3 is repeated twice. 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 above example, the first duplicate will be found at position 4. Assign index to another node temp. Connect index’s previous node with index’s next node. Delete temp which was pointing to duplicate node. This process will continue till all duplicates are removed.

Algorithm

Define a Node class which represents a node in the list. It will have three properties: data, previous which will point to the previous node and next which will point to the next node.
Define another class for creating a doubly linked list, and it has two nodes: head and tail. Initially, head and tail will point to null.
addNode() will add node to the list:
1. It first checks whether the head is null, then it will insert the node as the head.
2. Both head and tail will point to a newly added node.
3. Head’s previous pointer will point to null and tail’s next pointer will point to null.
4. If the head is not null, the new node will be inserted at the end of the list such that new node’s previous pointer will point to tail.
5. The new node will become the new tail. Tail’s next pointer will point to null.
removeDuplicateNode() will remove duplicate nodes from the list.
1. Define a new node current which will initially point to head.
2. Node index will always point to node next to current.
3. Loop through the list until current points to null.
4. Check whether current?s data is equal to index’s data that means index is duplicate of current.
5. Node temp will point to index to store duplicate node.
6. The previous node to the index will point to next node to index.
7. Since, temp is pointing to index, which is a duplicate node, so set temp to null.
display() will show all the nodes present in the list.
1. Define a new node ‘current’ that will point to the head.
2. Print current.data till current points to null.
3. Current will point to the next node in the list in each iteration.

Solution

Python

  #Represent a node of doubly linked list  class Node:      def __init__(self,data):          self.data = data;          self.previous = None;          self.next = None;            class RemoveDuplicate:      #Represent the head and tail of the doubly linked list      def __init__(self):          self.head = None;          self.tail = None;                #addNode() will add a node to the list      def addNode(self, data):          #Create a new node          newNode = Node(data);                    #If list is empty          if(self.head == None):              #Both head and tail will point to newNode              self.head = self.tail = newNode;              #head’s previous will point to None              self.head.previous = None;              #tail’s next will point to None, as it is the last node of the list              self.tail.next = None;          else:              #newNode will be added after tail such that tail’s next will point to newNode              self.tail.next = newNode;              #newNode’s previous will point to tail              newNode.previous = self.tail;              #newNode will become new tail              self.tail = newNode;              #As it is last node, tail’s next will point to None              self.tail.next = None;                    #removeDuplicateNode() will remove duplicate nodes from the list      def removeDuplicateNode(self):                    #Checks whether list is empty          if(self.head == None):              return;          else:              #Initially, current will point to head node              current = self.head;              while(current != None):                  #index will point to node next to current                  index = current.next                  while(index != None):                      if(current.data == index.data):                          #Store the duplicate node in temp                          temp = index;                          #index’s previous node will point to node next to index thus, removes the duplicate node                          index.previous.next = index.next;                          if(index.next != None):                              index.next.previous = index.previous;                          #Delete duplicate node by making temp to None                          temp = None;                      index = index.next;                  current = current.next;                                #display() will print out the nodes of 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;          print();            dList = RemoveDuplicate();  #Add nodes to the list  dList.addNode(1);  dList.addNode(2);  dList.addNode(3);  dList.addNode(2);  dList.addNode(2);  dList.addNode(4);  dList.addNode(5);  dList.addNode(3);     print(“Originals list: “);  dList.display();     #Removes duplicate nodes  dList.removeDuplicateNode();     print(“List after removing duplicates: “);  dList.display();  

Output:

Originals list:   1 2 3 2 2 4 5 3   List after removing duplicates:   1 2 3 4 5

C

  #include <stdio.h>     //Represent a node of the doubly linked list    struct node{      int data;      struct node *previous;      struct node *next;  };         //Represent the head and tail of the doubly linked list  struct node *head, *tail = NULL;     //addNode() will add a node to the list  void addNode(int data) {      //Create a new node      struct node *newNode = (struct node*)malloc(sizeof(struct node));      newNode->data = data;            //If list is empty      if(head == NULL) {          //Both head and tail will point to newNode          head = tail = newNode;          //head’s previous will point to NULL          head->previous = NULL;          //tail’s next will point to NULL, as it is the last node of the list          tail->next = NULL;      }      else {          //newNode will be added after tail such that tail’s next will point to newNode          tail->next = newNode;          //newNode’s previous will point to tail          newNode->previous = tail;          //newNode will become new tail          tail = newNode;          //As it is last node, tail’s next will point to NULL          tail->next = NULL;      }  }     //removeDuplicateNode() will remove duplicate nodes from the list  void removeDuplicateNode() {      //Node current will point to head      struct node *current, *index, *temp;            //Checks whether list is empty      if(head == NULL) {          return;      }      else {          //Initially, current will point to head node          for(current = head; current != NULL; current = current->next) {              //index will point to node next to current              for(index = current->next; index != NULL; index = index->next) {                  if(current->data == index->data) {                      //Store the duplicate node in temp                      temp = index;                      //index’s previous node will point to node next to index thus, removes the duplicate node                      index->previous->next = index->next;                      if(index->next != NULL)                          index->next->previous = index->previous;                      //Delete duplicate node by making temp to NULL                      temp = NULL;                  }              }          }      }  }     //display() will print out the nodes of the list  void display() {      //Node current will point to head      struct node *current = head;      if(head == NULL) {          printf(“List is emptyn”);          return;      }      while(current != NULL) {          //Prints each node by incrementing pointer.          printf(“%d “, current->data);          current = current->next;      }      printf(“n”);  }     int main()  {      //Add nodes to the list      addNode(1);      addNode(2);      addNode(3);      addNode(2);      addNode(2);      addNode(4);      addNode(5);      addNode(3);            printf(“Originals list: n”);      display();            //Removes duplicate nodes      removeDuplicateNode();            printf(“List after removing duplicates: n”);      display();         return 0;  }  

Output:

Originals list:   1 2 3 2 2 4 5 3   List after removing duplicates:   1 2 3 4 5

JAVA

  public class RemoveDuplicate {            //Represent a node of the doubly linked list        class Node{          int data;          Node previous;          Node next;                    public Node(int data) {              this.data = data;          }      }            //Represent the head and tail of the doubly linked list      Node head, tail = null;            //addNode() will add a node to the list      public void addNode(int data) {          //Create a new node          Node newNode = new Node(data);                    //If list is empty          if(head == null) {              //Both head and tail will point to newNode              head = tail = newNode;              //head’s previous will point to null              head.previous = null;              //tail’s next will point to null, as it is the last node of the list              tail.next = null;          }          else {              //newNode will be added after tail such that tail’s next will point to newNode              tail.next = newNode;              //newNode’s previous will point to tail              newNode.previous = tail;              //newNode will become new tail              tail = newNode;              //As it is last node, tail’s next will point to null              tail.next = null;          }      }            //removeDuplicateNode() will remove duplicate nodes from the list      public void removeDuplicateNode() {          //Node current will point to head          Node current, index, temp;                    //Checks whether list is empty          if(head == null) {              return;          }          else {              //Initially, current will point to head node              for(current = head; current != null; current = current.next) {                  //index will point to node next to current                  for(index = current.next; index != null; index = index.next) {                      if(current.data == index.data) {                          //Store the duplicate node in temp                          temp = index;                          //index’s previous node will point to node next to index thus, removes the duplicate node                          index.previous.next = index.next;                          if(index.next != null)                              index.next.previous = index.previous;                          //Delete duplicate node by making temp to null                          temp = null;                      }                  }              }          }      }            //display() will print out the nodes of 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 the pointer.                System.out.print(current.data + ” “);              current = current.next;          }          System.out.println();      }            public static void main(String[] args) {                    RemoveDuplicate dList = new RemoveDuplicate();          //Add nodes to the list          dList.addNode(1);          dList.addNode(2);          dList.addNode(3);          dList.addNode(2);          dList.addNode(2);          dList.addNode(4);          dList.addNode(5);          dList.addNode(3);                    System.out.println(“Originals list: “);          dList.display();                    //Removes duplicate nodes          dList.removeDuplicateNode();                    System.out.println(“List after removing duplicates: “);          dList.display();      }  }  

Output:

Originals list:   1 2 3 2 2 4 5 3   List after removing duplicates:   1 2 3 4 5

C#

  using System;   namespace DoublyLinkedList   {                           public class Program      {          //Represent a node of the doubly linked list            public class Node<T>{              public T data;              public Node<T> previous;              public Node<T> next;                            public Node(T value) {                  data = value;              }          }                    public class RemoveDuplicate<T>{              //Represent the head and tail of the doubly linked list              protected Node<T> head = null;                            protected Node<T> tail = null;                            //addNode() will add a node to the list              public void addNode(T data) {                  //Create a new node                  Node<T> newNode = new Node<T>(data);                     //If list is empty                  if(head == null) {                      //Both head and tail will point to newNode                      head = tail = newNode;                      //head’s previous will point to null                      head.previous = null;                      //tail’s next will point to null, as it is the last node of the list                      tail.next = null;                  }                  else {                      //newNode will be added after tail such that tail’s next will point to newNode                      tail.next = newNode;                      //newNode’s previous will point to tail                      newNode.previous = tail;                      //newNode will become new tail                      tail = newNode;                      //As it is last node, tail’s next will point to null                      tail.next = null;                  }              }                            //removeDuplicateNode() will remove duplicate nodes from the list              public void removeDuplicateNode() {                  //Node current will point to head                  Node<T> current, index, temp;                     //Checks whether list is empty                  if(head == null) {                      return;                  }                  else {                      //Initially, current will point to head node                      for(current = head; current != null; current = current.next) {                          //index will point to node next to current                          for(index = current.next; index != null; index = index.next) {                              if(current.data.Equals(index.data)) {                                  //Store the duplicate node in temp                                  temp = index;                                  //index’s previous node will point to node next to index thus, removes the duplicate node                                  index.previous.next = index.next;                                  if(index.next != null)                                      index.next.previous = index.previous;                                  //Delete duplicate node by making temp to null                                  temp = null;                              }                          }                      }                  }              }                    //display() will print out the nodes of 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 the pointer.                        Console.Write(current.data + ” “);                      current = current.next;                  }                  Console.WriteLine();              }          }                    public static void Main()          {              RemoveDuplicate<int> dList = new RemoveDuplicate<int>();              //Add nodes to the list              dList.addNode(1);              dList.addNode(2);              dList.addNode(3);              dList.addNode(2);              dList.addNode(2);              dList.addNode(4);              dList.addNode(5);              dList.addNode(3);                 Console.WriteLine(“Originals list: “);              dList.display();                 //Removes duplicate nodes              dList.removeDuplicateNode();                 Console.WriteLine(“List after removing duplicates: “);              dList.display();          }          }  }  

Output:

Originals list:   1 2 3 2 2 4 5 3   List after removing duplicates:   1 2 3 4 5

PHP

  <!DOCTYPE html>  <html>  <body>  <?php  //Represent a node of doubly linked list  class Node{      public $data;      public $previous;      public $next;            function __construct($data){          $this->data = $data;      }  }  class RemoveDuplicate{      //Represent the head and tail of the doubly linked list      public $head;      public $tail;      function __construct(){          $this->head = NULL;          $this->tail = NULL;      }            //addNode() will add a node to the list      function addNode($data){          //Create a new node          $newNode = new Node($data);                    //If list is empty          if($this->head == NULL) {              //Both head and tail will point to newNode              $this->head = $this->tail = $newNode;              //head’s previous will point to NULL              $this->head->previous = NULL;              //tail’s next will point to NULL, as it is the last node of the list              $this->tail->next = NULL;          }          else {              //newNode will be added after tail such that tail’s next will point to newNode              $this->tail->next = $newNode;              //newNode’s previous will point to tail              $newNode->previous = $this->tail;              //newNode will become new tail              $this->tail = $newNode;              //As it is last node, tail’s next will point to NULL              $this->tail->next = NULL;          }      }            //removeDuplicateNode() will remove duplicate nodes from the list      function removeDuplicateNode() {                  //Checks whether list is empty          if($this->head == NULL) {              return;          }          else {              //Initially, current will point to head node              for($current = $this->head; $current != NULL; $current = $current->next) {                  //index will point to node next to current                  for($index = $current->next; $index != NULL; $index = $index->next) {                      if($current->data == $index->data) {                          //Store the duplicate node in temp                          $temp = $index;                          //index’s previous node will point to node next to index thus, removes the duplicate node                          $index->previous->next = $index->next;                          if($index->next != NULL)                              $index->next->previous = $index->previous;                          //Delete duplicate node by making temp to NULL                          $temp = NULL;                      }                  }              }          }      }            //display() will print out the nodes of 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>”);      }  }        $dList = new RemoveDuplicate();  //Add nodes to the list  $dList->addNode(1);  $dList->addNode(2);  $dList->addNode(3);  $dList->addNode(2);  $dList->addNode(2);  $dList->addNode(4);  $dList->addNode(5);  $dList->addNode(3);     print(“Originals list: <br>”);  $dList->display();     //Removes duplicate nodes  $dList->removeDuplicateNode();     print(“List after removing duplicates: <br>”);  $dList->display();  ?>  </body>  </html>  

Output:

Originals list:   1 2 3 2 2 4 5 3   List after removing duplicates:   1 2 3 4 5

Next Topic#

Q. Program to remove duplicate elements from a doubly linked list.

Explanation

Algorithm

Solution

Python

C

JAVA

C#

PHP

Wind Energy

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