# Remove duplicates from a sorted linked list using recursion

• Difficulty Level : Easy
• Last Updated : 24 Jun, 2021

Write a removeDuplicates() function which takes a list sorted in non-decreasing order and deletes any duplicate nodes from the list. The list should only be traversed once.
For example if the linked list is 11->11->11->21->43->43->60 then removeDuplicates() should convert the list to 11->21->43->60.

Algorithm:
Traverse the list recursively from the head (or start) to end and after completion of recursion calls, compare the next node(returned node) and current node(head). If data of both nodes are equal then return the next (head-> next) node else return the current node(head).
Implementation:
Functions other than removeDuplicates() are just to create a linked linked list and test removeDuplicates().

## C++

 `/* C Program to remove duplicates` ` ``from a sorted linked list */` `#include ` `#include `   `/* Link list node */` `struct` `Node {` `    ``int` `data;` `    ``struct` `Node* next;` `};`   `/* The function removes duplicates from a sorted list */` `struct` `Node* removeDuplicates(``struct` `Node* head)` `{` `    ``/* if head is null then return*/` `    ``if` `(head == NULL)` `        ``return` `NULL;`   `    ``/* Remove duplicates from list after head */` `    ``head->next = removeDuplicates(head->next);`   `    ``// Check if head itself is duplicate` `    ``if` `(head->next != NULL && ` `        ``head->next->data == head->data) {`   `        ``Node* res = head->next;` `        ``delete` `head;` `        ``return` `res;` `    ``}`   `    ``return` `head;` `}`   `/* UTILITY FUNCTIONS */` `/* Function to insert a node at ` `   ``the beginning of the linked list */` `void` `push(``struct` `Node** head_ref, ``int` `new_data)` `{` `    ``struct` `Node* new_node = ``new` `Node;` `    ``new_node->data = new_data;` `    ``new_node->next = (*head_ref);` `    ``(*head_ref) = new_node;` `}`   `/* Function to print nodes in a given linked list */` `void` `printList(``struct` `Node* node)` `{` `    ``while` `(node != NULL) {` `        ``printf``(``"%d "``, node->data);` `        ``node = node->next;` `    ``}` `}`   `/* Driver program to test above functions*/` `int` `main()` `{` `    ``/* Start with the empty list */` `    ``struct` `Node* head = NULL;`   `    ``/* Let us create a sorted linked list to test the functions` `    ``Created linked list will be 11->11->11->13->13->20 */` `    ``push(&head, 20);` `    ``push(&head, 13);` `    ``push(&head, 13);` `    ``push(&head, 11);` `    ``push(&head, 11);` `    ``push(&head, 11);`   `    ``printf``(``"\n Linked list before duplicate removal "``);` `    ``printList(head);`   `    ``/* Remove duplicates from linked list */` `    ``struct` `Node* h = removeDuplicates(head);`   `    ``printf``(``"\n Linked list after duplicate removal "``);` `    ``printList(h);`   `    ``return` `0;` `}`

## Java

 `/* Java Program to remove duplicates ` `from a sorted linked list */` `class` `GFG ` `{`   `/* Link list node */` `static` `class` `Node ` `{ ` `    ``int` `data; ` `    ``Node next; ` `}; `   `/* The function removes duplicates from a sorted list */` `static` `Node removeDuplicates( Node head) ` `{ ` `    ``/* if head is null then return*/` `    ``if` `(head == ``null``) ` `        ``return` `null``; `   `    ``/* Remove duplicates from list after head */` `    ``head.next = removeDuplicates(head.next); `   `    ``// Check if head itself is duplicate ` `    ``if` `(head.next != ``null` `&& ` `        ``head.next.data == head.data)` `    ``{ `   `        ``Node res = head.next; ` `        `  `        ``return` `res; ` `    ``} `   `    ``return` `head; ` `} `   `/* UTILITY FUNCTIONS */` `/* Function to insert a node at ` `the beginning of the linked list */` `static` `Node push( Node head_ref, ``int` `new_data) ` `{ ` `    ``Node new_node = ``new` `Node(); ` `    ``new_node.data = new_data; ` `    ``new_node.next = (head_ref); ` `    ``(head_ref) = new_node;` `    ``return` `head_ref;` `} `   `/* Function to print nodes in a given linked list */` `static` `void` `printList( Node node) ` `{ ` `    ``while` `(node != ``null``) ` `    ``{ ` `        ``System.out.printf(``"%d "``, node.data); ` `        ``node = node.next; ` `    ``} ` `} `   `/* Driver program to test above functions*/` `public` `static` `void` `main(String args[]) ` `{ ` `    ``/* Start with the empty list */` `    ``Node head = ``null``; `   `    ``/* Let us create a sorted linked list to test the functions ` `    ``Created linked list will be 11.11.11.13.13.20 */` `    ``head = push(head, ``20``); ` `    ``head = push(head, ``13``); ` `    ``head = push(head, ``13``); ` `    ``head = push(head, ``11``); ` `    ``head = push(head, ``11``); ` `    ``head = push(head, ``11``); `   `    ``System.out.printf(``"\n Linked list before duplicate removal "``); ` `    ``printList(head); `   `    ``/* Remove duplicates from linked list */` `    ``Node h = removeDuplicates(head); `   `    ``System.out.printf(``"\n Linked list after duplicate removal "``); ` `    ``printList(h); ` `}` `} `   `// This code is contributed by Arnab Kundu`

## Python

 `# Python Program to remove duplicates ` `# from a sorted linked list `   `# A linked list node` `class` `Node: ` `    ``def` `__init__(``self``, new_data): ` `        ``self``.data ``=` `new_data ` `        ``self``.``next` `=` `None`   `# The function removes duplicates from a sorted list ` `def` `removeDuplicates( head) :`   `    ``# if head is None then return` `    ``if` `(head ``=``=` `None``) :` `        ``return` `None`   `    ``# Remove duplicates from list after head ` `    ``head.``next` `=` `removeDuplicates(head.``next``) `   `    ``# Check if head itself is duplicate ` `    ``if` `(head.``next` `!``=` `None` `and` `        ``head.``next``.data ``=``=` `head.data):` `        ``res ``=` `head.``next` `        `  `        ``return` `res ` `    `  `    ``return` `head `   `# UTILITY FUNCTIONS ` `# Function to insert a node at ` `#the beginning of the linked list ` `def` `push( head_ref, new_data) :` `    ``new_node ``=` `Node(``0``) ` `    ``new_node.data ``=` `new_data ` `    ``new_node.``next` `=` `(head_ref) ` `    ``(head_ref) ``=` `new_node` `    ``return` `head_ref`   `# Function to print nodes in a given linked list ` `def` `printList(node) :`   `    ``while` `(node !``=` `None``) :` `    `  `        ``print``(node.data,end``=``" "``) ` `        ``node ``=` `node.``next` `    `  `# Driver program to test above functions`   `# Start with the empty list ` `head ``=` `None`   `# Let us create a sorted linked list to test the functions ` `# Created linked list will be 11.11.11.13.13.20 ` `head ``=` `push(head, ``20``) ` `head ``=` `push(head, ``13``) ` `head ``=` `push(head, ``13``) ` `head ``=` `push(head, ``11``) ` `head ``=` `push(head, ``11``) ` `head ``=` `push(head, ``11``) `   `print``(``"\n Linked list before duplicate removal "``) ` `printList(head) `   `# Remove duplicates from linked list ` `h ``=` `removeDuplicates(head) `   `print``(``"\n Linked list after duplicate removal "``) ` `printList(h) `   `# This code is contributed by Arnab Kundu`

## C#

 `/* C# Program to remove duplicates ` `from a sorted linked list */` `using` `System;`   `class` `GFG ` `{` `    `  `    ``/* Link list node */` `    ``public` `class` `Node ` `    ``{ ` `        ``public` `int` `data; ` `        ``public` `Node next; ` `    ``}; ` `    `  `    ``/* The function removes duplicates from a sorted list */` `    ``static` `Node removeDuplicates( Node head) ` `    ``{ ` `        ``/* if head is null then return*/` `        ``if` `(head == ``null``) ` `            ``return` `null``; ` `    `  `        ``/* Remove duplicates from list after head */` `        ``head.next = removeDuplicates(head.next); ` `    `  `        ``// Check if head itself is duplicate ` `        ``if` `(head.next != ``null` `&& ` `            ``head.next.data == head.data)` `        ``{ ` `    `  `            ``Node res = head.next; ` `            `  `            ``return` `res; ` `        ``} ` `    `  `        ``return` `head; ` `    ``} ` `    `  `    ``/* UTILITY FUNCTIONS */` `    ``/* Function to insert a node at ` `    ``the beginning of the linked list */` `    ``static` `Node push( Node head_ref, ``int` `new_data) ` `    ``{ ` `        ``Node new_node = ``new` `Node(); ` `        ``new_node.data = new_data; ` `        ``new_node.next = (head_ref); ` `        ``(head_ref) = new_node;` `        ``return` `head_ref;` `    ``} ` `    `  `    ``/* Function to print nodes in a given linked list */` `    ``static` `void` `printList( Node node) ` `    ``{ ` `        ``while` `(node != ``null``) ` `        ``{ ` `            ``Console.Write(``"{0} "``, node.data); ` `            ``node = node.next; ` `        ``} ` `    ``} ` `    `  `    ``/* Driver program to test above functions*/` `    ``public` `static` `void` `Main(String []args) ` `    ``{ ` `        ``/* Start with the empty list */` `        ``Node head = ``null``; ` `    `  `        ``/* Let us create a sorted linked list to test the functions ` `        ``Created linked list will be 11.11.11.13.13.20 */` `        ``head = push(head, 20); ` `        ``head = push(head, 13); ` `        ``head = push(head, 13); ` `        ``head = push(head, 11); ` `        ``head = push(head, 11); ` `        ``head = push(head, 11); ` `    `  `        ``Console.Write(``"\n Linked list before duplicate removal "``); ` `        ``printList(head); ` `    `  `        ``/* Remove duplicates from linked list */` `        ``Node h = removeDuplicates(head); ` `    `  `        ``Console.Write(``"\n Linked list after duplicate removal "``); ` `        ``printList(h); ` `    ``}` `}`   `/* This code contributed by PrinciRaj1992 */`

## Javascript

 ``

Output:

```Linked list before duplicate removal 11 11 11 13 13 20
Linked list after duplicate removal 11 13 20```

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