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

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.

Algorithm:

• Create a function named “push” which takes one Node value and one integer value as input with the node return type.
• “push” will add a new node in the front of the linked list.
•  Create a function named “deleteNode” which take two Node value as input parameters with the Node return type.
• “deleteNode” will delete the given node.
• Create a function “deletesmallerNodes” which takes one node value and one integer value as input parameter with node                  return type.
•  Initialize two Node pointers – ptr and next, both pointing to the head node of the Doubly Linked List.
• Start a while loop till ptr is not equal to null.
  •  If the current node’s data (ptr) is smaller than the specified value K, call the deleteNode function to delete the current node from the Doubly Linked List.
  •  Move the ptr to the next node in the Doubly Linked List.
• Return the head_ref pointer after all the nodes smaller than K are deleted.

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 <bits/stdc++.h>

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 of 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 of 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 of 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 --> pointer to head node pointer.
# del --> pointer 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 print nodes in a
# given doubly linked list
def printList(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 = "")
    printList(head)

    deletesmallerNodes(head, K)

    print("\nModified List: ", end = "")
    printList(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 of 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

<script>

// JavaScript implementation to delete all
// the nodes from the doubly
// linked list that are smaller than
// the specified value K
// Node of the doubly linked list
class Node {
    constructor(val) {
        this.data = val;
        this.prev = null;
        this.next = null;
    }
}
    // function to insert a node at the beginning
    // of the Doubly Linked List
    function push(head_ref , new_data) {
        // allocate node
     var 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 of 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
    function deleteNode(head_ref,  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
    function deletesmallerNodes(head_ref , K) {
     var ptr = head_ref;
     var 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
    function printList(head) {
        while (head != null) {
            document.write(head.data + " ");
            head = head.next;
        }
    }

    // Driver code

        // start with the empty list
        var 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);

        var K = 10;

        document.write("Original List: ");
        printList(head);

        head = deletesmallerNodes(head, K);

        document.write("<br/>Modified List: ");
        printList(head);

// This code contributed by umadevi9616

</script>

Output

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

Complexity Analysis:

• Time Complexity: O(N), where N is the total number of Nodes.
• Space Complexity: O(1) because using constant variables