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# Delete all the nodes from a doubly linked list that are smaller than a given value

• Difficulty Level : Medium
• Last Updated : 27 May, 2021

Given a doubly linked list containing N nodes and a number K, the task is to delete all the nodes from the list that are smaller than the given value K.
Examples:

```Input: 15 <=> 16 <=> 10 <=> 9 <=> 6 <=> 7 <=> 17
K = 10
Output: 15 <=> 16 <=> 10 <=> 17

Input: 5 <=> 3 <=> 6 <=> 8 <=> 4 <=> 1 <=> 2 <=> 9
K = 4
Output: 5 <=> 6 <=> 8 <=> 4 <=> 9```

Approach: Traverse the nodes of the doubly linked list one by one and get the pointer of the nodes having data value smaller than K. Refer to the article on Deleting a node from Doubly Linked List to delete a node.
Below is the implementation of the above approach:

## C++

 `// C++ implementation to delete all``// the nodes from the doubly``// linked list that are smaller than``// the specified value K``#include ` `using` `namespace` `std;` `// Node of the doubly linked list``struct` `Node {``    ``int` `data;``    ``Node *prev, *next;``};` `// function to insert a node at the beginning``// of the Doubly Linked List``void` `push(Node** head_ref, ``int` `new_data)``{``    ``// allocate node``    ``Node* new_node = (Node*)``malloc``(``sizeof``(``struct` `Node));` `    ``// put in the data``    ``new_node->data = new_data;` `    ``// since we are adding at the beginning,``    ``// prev is always NULL``    ``new_node->prev = NULL;` `    ``// link the old list off the new node``    ``new_node->next = (*head_ref);` `    ``// change prev of head node to new node``    ``if` `((*head_ref) != NULL)``        ``(*head_ref)->prev = new_node;` `    ``// move the head to point to the new node``    ``(*head_ref) = new_node;``}` `// function to delete a node in a Doubly Linked List.``// head_ref --> pointer to head node pointer.``// del  -->  pointer to node to be deleted``void` `deleteNode(Node** head_ref, Node* del)``{``    ``// base case``    ``if` `(*head_ref == NULL || del == NULL)``        ``return``;` `    ``// If node to be deleted is head node``    ``if` `(*head_ref == del)``        ``*head_ref = del->next;` `    ``// Change next only if node to be``    ``// deleted is NOT the last node``    ``if` `(del->next != NULL)``        ``del->next->prev = del->prev;` `    ``// Change prev only if node to be``    ``// deleted is NOT the first node``    ``if` `(del->prev != NULL)``        ``del->prev->next = del->next;` `    ``// Finally, free the memory occupied by del``    ``free``(del);` `    ``return``;``}` `// function to delete all the nodes``// from the doubly linked``// list that are smaller than the``// specified value K``void` `deletesmallerNodes(Node** head_ref, ``int` `K)``{``    ``Node* ptr = *head_ref;``    ``Node* next;` `    ``while` `(ptr != NULL) {``        ``next = ptr->next;``        ``// if true, delete node 'ptr'``        ``if` `(ptr->data < K)``            ``deleteNode(head_ref, ptr);``        ``ptr = next;``    ``}``}` `// function to print nodes in a``// given doubly linked list``void` `printList(Node* head)``{``    ``while` `(head != NULL) {``        ``cout << head->data << ``" "``;``        ``head = head->next;``    ``}``}` `// Driver program to test above``int` `main()``{``    ``// start with the empty list``    ``Node* head = NULL;` `    ``// create the doubly linked list``    ``// 15 <-> 16 <-> 10 <-> 9 <-> 6 <-> 7 <-> 17``    ``push(&head, 17);``    ``push(&head, 7);``    ``push(&head, 6);``    ``push(&head, 9);``    ``push(&head, 10);``    ``push(&head, 16);``    ``push(&head, 15);` `    ``int` `K = 10;` `    ``cout << ``"Original List: "``;``    ``printList(head);` `    ``deletesmallerNodes(&head, K);` `    ``cout << ``"\nModified List: "``;``    ``printList(head);``}`

## Java

 `// Java implementation to delete all``// the nodes from the doubly``// linked list that are smaller than``// the specified value K``class` `GFG``{``    ` `// Node of the doubly linked list``static` `class` `Node``{``    ``int` `data;``    ``Node prev, next;``};` `// function to insert a node at the beginning``// of the Doubly Linked List``static` `Node push(Node head_ref, ``int` `new_data)``{``    ``// allocate node``    ``Node new_node =``new` `Node();` `    ``// put in the data``    ``new_node.data = new_data;` `    ``// since we are adding at the beginning,``    ``// prev is always null``    ``new_node.prev = ``null``;` `    ``// link the old list off the new node``    ``new_node.next = (head_ref);` `    ``// change prev of head node to new node``    ``if` `((head_ref) != ``null``)``        ``(head_ref).prev = new_node;` `    ``// move the head to point to the new node``    ``(head_ref) = new_node;``    ` `    ``return` `head_ref;``}` `// function to delete a node in a Doubly Linked List.``// head_ref -. pointer to head node pointer.``// del -. pointer to node to be deleted``static` `Node deleteNode(Node head_ref, Node del)``{``    ``// base case``    ``if` `(head_ref == ``null` `|| del == ``null``)``        ``return` `null``;` `    ``// If node to be deleted is head node``    ``if` `(head_ref == del)``        ``head_ref = del.next;` `    ``// Change next only if node to be``    ``// deleted is NOT the last node``    ``if` `(del.next != ``null``)``        ``del.next.prev = del.prev;` `    ``// Change prev only if node to be``    ``// deleted is NOT the first node``    ``if` `(del.prev != ``null``)``        ``del.prev.next = del.next;` `    ``return` `head_ref;``}` `// function to delete all the nodes``// from the doubly linked``// list that are smaller than the``// specified value K``static` `Node deletesmallerNodes(Node head_ref, ``int` `K)``{``    ``Node ptr = head_ref;``    ``Node next;` `    ``while` `(ptr != ``null``)``    ``{``        ``next = ptr.next;``        ` `        ``// if true, delete node 'ptr'``        ``if` `(ptr.data < K)``            ``deleteNode(head_ref, ptr);``        ``ptr = next;``    ``}``    ``return` `head_ref;``}` `// function to print nodes in a``// given doubly linked list``static` `void` `printList(Node head)``{``    ``while` `(head != ``null``)``    ``{``        ``System.out.print( head.data + ``" "``);``        ``head = head.next;``    ``}``}` `// Driver code``public` `static` `void` `main(String args[])``{``    ``// start with the empty list``    ``Node head = ``null``;` `    ``// create the doubly linked list``    ``// 15 <. 16 <. 10 <. 9 <. 6 <. 7 <. 17``    ``head=push(head, ``17``);``    ``head=push(head, ``7``);``    ``head=push(head, ``6``);``    ``head=push(head, ``9``);``    ``head=push(head, ``10``);``    ``head=push(head, ``16``);``    ``head=push(head, ``15``);` `    ``int` `K = ``10``;` `    ``System.out.print(``"Original List: "``);``    ``printList(head);` `    ``head=deletesmallerNodes(head, K);` `    ``System.out.print(``"\nModified List: "``);``    ``printList(head);``}``}` `// This code is contributed by Arnab Kundu`

## Python3

 `# Python3 implementation to delete all``# the nodes from the doubly``# linked list that are smaller than``# the specified value K``import` `math` `# Node of the doubly linked list``class` `Node:``    ``def` `__init__(``self``, data):``        ``self``.data ``=` `data``        ``self``.``next` `=` `None` `# function to insert a node at the beginning``# of the Doubly Linked List``def` `push(head_ref, new_data):``    ` `    ``# allocate node``    ``new_node ``=` `Node(new_data)` `    ``# put in the data``    ``new_node.data ``=` `new_data` `    ``# since we are adding at the beginning,``    ``# prev is always None``    ``new_node.prev ``=` `None` `    ``# link the old list off the new node``    ``new_node.``next` `=` `head_ref` `    ``# change prev of head node to new node``    ``if` `(head_ref !``=` `None``):``        ``head_ref.prev ``=` `new_node` `    ``# move the head to po to the new node``    ``head_ref ``=` `new_node``    ``return` `head_ref` `# function to delete a node in a Doubly Linked List.``# head_ref --> poer to head node poer.``# del --> poer to node to be deleted``def` `deleteNode(head_ref, delete):``    ` `    ``# base case``    ``if` `(head_ref ``=``=` `None` `or` `delete ``=``=` `None``):``        ``return` `None` `    ``# If node to be deleted is head node``    ``if` `(head_ref ``=``=` `delete):``        ``head_ref ``=` `delete.``next` `    ``# Change next only if node to be``    ``# deleted is NOT the last node``    ``if` `(delete.``next` `!``=` `None``):``        ``delete.``next``.prev ``=` `delete.prev` `    ``# Change prev only if node to be``    ``# deleted is NOT the first node``    ``if` `(delete.prev !``=` `None``):``        ``delete.prev.``next` `=` `delete.``next` `    ``# Finally, free the memory occupied by del``    ``# free(delete)``    ``return` `head_ref` `# function to delete all the nodes``# from the doubly linked``# list that are smaller than the``# specified value K``def` `deletesmallerNodes(head_ref, K):``    ``ptr ``=` `head_ref``    ``next` `=` `None` `    ``while` `(ptr !``=` `None``) :``        ``next` `=` `ptr.``next``        ` `        ``# if true, delete node 'ptr'``        ``if` `(ptr.data < K):``            ``deleteNode(head_ref, ptr)``        ``ptr ``=` `next``    ` `# function to pr nodes in a``# given doubly linked list``def` `prList(head):``    ``while` `(head !``=` `None``):``        ``print``(head.data, end ``=` `" "``)``        ``head ``=` `head.``next` `# Driver Code``if` `__name__``=``=``'__main__'``:``    ` `    ``# start with the empty list``    ``head ``=` `None` `    ``# create the doubly linked list``    ``# 15 <. 16 <. 10 <. 9 <. 6 <. 7 <. 17``    ``head ``=` `push(head, ``17``)``    ``head ``=` `push(head, ``7``)``    ``head ``=` `push(head, ``6``)``    ``head ``=` `push(head, ``9``)``    ``head ``=` `push(head, ``10``)``    ``head ``=` `push(head, ``16``)``    ``head ``=` `push(head, ``15``)` `    ``K ``=` `10` `    ``print``(``"Original List: "``, end ``=` `"")``    ``prList(head)` `    ``deletesmallerNodes(head, K)` `    ``print``(``"\nModified List: "``, end ``=` `"")``    ``prList(head)` `# This code is contributed by AbhiThakur`

## C#

 `// C# implementation to delete all``// the nodes from the doubly``// linked list that are smaller than``// the specified value K``using` `System;` `class` `GFG``{``    ` `// Node of the doubly linked list``public` `class` `Node``{``    ``public` `int` `data;``    ``public` `Node prev, next;``};` `// function to insert a node at the beginning``// of the Doubly Linked List``static` `Node push(Node head_ref, ``int` `new_data)``{``    ``// allocate node``    ``Node new_node = ``new` `Node();` `    ``// put in the data``    ``new_node.data = new_data;` `    ``// since we are adding at the beginning,``    ``// prev is always null``    ``new_node.prev = ``null``;` `    ``// link the old list off the new node``    ``new_node.next = (head_ref);` `    ``// change prev of head node to new node``    ``if` `((head_ref) != ``null``)``        ``(head_ref).prev = new_node;` `    ``// move the head to point to the new node``    ``(head_ref) = new_node;``    ` `    ``return` `head_ref;``}` `// function to delete a node in a Doubly Linked List.``// head_ref -. pointer to head node pointer.``// del -. pointer to node to be deleted``static` `Node deleteNode(Node head_ref, Node del)``{``    ``// base case``    ``if` `(head_ref == ``null` `|| del == ``null``)``        ``return` `null``;` `    ``// If node to be deleted is head node``    ``if` `(head_ref == del)``        ``head_ref = del.next;` `    ``// Change next only if node to be``    ``// deleted is NOT the last node``    ``if` `(del.next != ``null``)``        ``del.next.prev = del.prev;` `    ``// Change prev only if node to be``    ``// deleted is NOT the first node``    ``if` `(del.prev != ``null``)``        ``del.prev.next = del.next;` `    ``return` `head_ref;``}` `// function to delete all the nodes``// from the doubly linked``// list that are smaller than the``// specified value K``static` `Node deletesmallerNodes(Node head_ref, ``int` `K)``{``    ``Node ptr = head_ref;``    ``Node next;` `    ``while` `(ptr != ``null``)``    ``{``        ``next = ptr.next;``        ` `        ``// if true, delete node 'ptr'``        ``if` `(ptr.data < K)``            ``deleteNode(head_ref, ptr);``        ``ptr = next;``    ``}``    ``return` `head_ref;``}` `// function to print nodes in a``// given doubly linked list``static` `void` `printList(Node head)``{``    ``while` `(head != ``null``)``    ``{``        ``Console.Write( head.data + ``" "``);``        ``head = head.next;``    ``}``}` `// Driver code``public` `static` `void` `Main(String []args)``{``    ``// start with the empty list``    ``Node head = ``null``;` `    ``// create the doubly linked list``    ``// 15 <. 16 <. 10 <. 9 <. 6 <. 7 <. 17``    ``head = push(head, 17);``    ``head = push(head, 7);``    ``head = push(head, 6);``    ``head = push(head, 9);``    ``head = push(head, 10);``    ``head = push(head, 16);``    ``head = push(head, 15);` `    ``int` `K = 10;` `    ``Console.Write(``"Original List: "``);``    ``printList(head);` `    ``head=deletesmallerNodes(head, K);` `    ``Console.Write(``"\nModified List: "``);``    ``printList(head);``}``}` `// This code contributed by Rajput-Ji`

## Javascript

 ``

Output:

```Original List: 15 16 10 9 6 7 17
Modified List: 15 16 10 17```

Time Complexity: O(N), where N is the total number of Nodes.

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