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.



Below is the implementation of the above approach:

C++

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// 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 begining,
    // 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);
}

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Java

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// 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 begining, 
    // 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

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Python3

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# 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 begining,
    # 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

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C#

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// 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 begining, 
    // 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

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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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