Delete linked list nodes which have a Lesser Value on Left Side

Given a singly linked list, the task is to remove all the nodes which have a lesser value on left side.

Examples:

Input: 12->15->10->11->5->6->2->3
Output: Modified Linked List = 12 -> 10 -> 5 -> 2 

Input: 25->15->6->48->12->5->16->14
Output: Modified Linked List = 25 -> 15 -> 6 -> 5

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach:

Initialize a varaible maximum with head node.
Traverse the list.
Check if the next node is lesser than max_node. If yes, the move to the next node.
Else If not, then update the value of max_node and delete the next node.

Below is the implementation of above approach:

C++

// C++ implementation of above approach 
#include <bits/stdc++.h> 
using namespace std; 
  
// Structure of a linked list node 
struct Node { 
    int data; 
    struct Node* next; 
}; 
  
// Function to Delete nodes which have 
// greater value node(s) on right side 
void delNodes(struct Node* head) 
{ 
    struct Node* current = head; 
  
    // Initialize max 
    struct Node* maxnode = head; 
    struct Node* temp; 
  
    while (current != NULL && current->next != NULL) { 
  
        // If current is greater than max, 
        // then update max and move current 
        if (current->next->data <= maxnode->data) { 
            current = current->next; 
            maxnode = current; 
        } 
  
        // If current is smaller than max, then delete current 
        else { 
            temp = current->next; 
            current->next = temp->next; 
            free(temp); 
        } 
    } 
} 
  
/* Utility function to insert a node at the beginning */
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; 
} 
  
/* Utility function to print a linked list */
void printList(struct Node* head) 
{ 
    while (head != NULL) { 
        cout << head->data << " "; 
        head = head->next; 
    } 
    cout << endl; 
} 
  
/* Driver program to test above functions */
int main() 
{ 
    struct Node* head = NULL; 
  
    /* Create following linked list  
    12->15->10->11->5->6->2->3 */
    push(&head, 3); 
    push(&head, 2); 
    push(&head, 6); 
    push(&head, 5); 
    push(&head, 11); 
    push(&head, 10); 
    push(&head, 15); 
    push(&head, 12); 
  
    printf("Given Linked List: "); 
    printList(head); 
  
    delNodes(head); 
  
    printf("\nModified Linked List: "); 
    printList(head); 
  
    return 0; 
} 

Java

// Java implementation of above approach  
class Solution 
{ 
  
// Structure of a linked list node  
static class Node  
{  
    int data;  
    Node next;  
};  
  
// Function to Delete nodes which have  
// greater value node(s) on right side  
static Node delNodes(Node head)  
{  
    Node current = head;  
  
    // Initialize max  
    Node maxnode = head;  
    Node temp;  
  
    while (current != null && current.next != null) 
    {  
  
        // If current is lesser than max,  
        // then update max and move current  
        if (current.next.data <= maxnode.data)  
        {  
            current = current.next;  
            maxnode = current;  
        }  
  
        // If current is greater than max, then delete current  
        else
        {  
            temp = current.next;  
            current.next = temp.next;  
        }  
    }  
    return head; 
}  
  
  
// Utility function to insert a node at the beginning / 
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; 
}  
  
// Utility function to print a linked list / 
static Node printList(Node head)  
{  
    while (head != null) 
    {  
        System.out.print( head.data + " ");  
        head = head.next;  
    }  
    System.out.println(); 
    return head; 
}  
  
// Driver program to test above functions / 
public static void main(String args[])  
{  
    Node head = null;  
  
    /* Create following linked list  
    12->15->10->11->5->6->2->3 */
    head=push(head, 3);  
    head=push(head, 2);  
    head=push(head, 6);  
    head=push(head, 5);  
    head=push(head, 11);  
    head=push(head, 10);  
    head=push(head, 15);  
    head=push(head, 12);  
  
    System.out.printf("Given Linked List \n");  
    printList(head);  
  
    head=delNodes(head);  
  
    System.out.printf("Modified Linked List \n");  
    printList(head);  
} 
}  
  
// This code is contributed by Arnab Kundu 

Python3

# Python implementation of above approach 
import math 
  
# Structure of a linked list node 
class Node:  
    def __init__(self, data):  
        self.data = data  
        self.next = None
  
# Function to Delete nodes which have 
# greater value node(s) on right side 
def delNodes(head): 
    current = head 
  
    # Initialize max 
    maxnode = head 
    temp = None
  
    while (current != None and current.next != None): 
  
        # If current is greater than max, 
        # then update max and move current 
        if (current.next.data <= maxnode.data): 
            current = current.next
            maxnode = current 
          
        # If current is smaller than max,  
        # then delete current 
        else: 
            temp = current.next
            current.next = temp.next
            #free(temp) 
      
# Utility function to insert a node at the beginning  
def push(head_ref, new_data): 
    new_node = Node(new_data) 
    new_node.data = new_data 
    new_node.next = head_ref 
    head_ref = new_node 
    return head_ref 
  
# Utility function to print a linked list  
def printList(head): 
    while (head != None) : 
        print(head.data, end = " ") 
        head = head.next
    print() 
      
# Driver Code 
if __name__=='__main__':  
    head = None
  
    # Create following linked list  
    # 12.15.10.11.5.6.2.3  
    head = push(head, 3) 
    head = push(head, 2) 
    head = push(head, 6) 
    head = push(head, 5) 
    head = push(head, 11) 
    head = push(head, 10) 
    head = push(head, 15) 
    head = push(head, 12) 
  
    print("Given Linked List: ", end = "") 
    printList(head) 
  
    delNodes(head) 
  
    print("\nModified Linked List: ", end = "") 
    printList(head) 
  
# This code is contributed by AbhiThakur 

C#

// C# implementation of the above approach:  
using System; 
class GFG 
{ 
  
// Structure of a linked list node  
public class Node  
{  
    public int data;  
    public Node next;  
};  
  
// Function to Delete nodes which have  
// greater value node(s) on right side  
static Node delNodes(Node head)  
{  
    Node current = head;  
  
    // Initialize max  
    Node maxnode = head;  
    Node temp;  
  
    while (current != null && 
           current.next != null) 
    {  
  
        // If current is lesser than max,  
        // then update max and move current  
        if (current.next.data <= maxnode.data)  
        {  
            current = current.next;  
            maxnode = current;  
        }  
  
        // If current is greater than max,  
        // then delete current  
        else
        {  
            temp = current.next;  
            current.next = temp.next;  
        }  
    }  
    return head; 
}  
  
// Utility function to insert  
// a node at the beginning  
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; 
}  
  
// Utility function to print a linked list  
static Node printList(Node head)  
{  
    while (head != null) 
    {  
        Console.Write(head.data + " ");  
        head = head.next;  
    }  
    Console.WriteLine(); 
    return head; 
}  
  
// Driver Code 
public static void Main(String []args)  
{  
    Node head = null;  
  
    /* Create following linked list  
    12->15->10->11->5->6->2->3 */
    head = push(head, 3);  
    head = push(head, 2);  
    head = push(head, 6);  
    head = push(head, 5);  
    head = push(head, 11);  
    head = push(head, 10);  
    head = push(head, 15);  
    head = push(head, 12);  
  
    Console.Write("Given Linked List \n");  
    printList(head);  
  
    head = delNodes(head);  
  
    Console.Write("Modified Linked List \n");  
    printList(head);  
} 
}  
  
// This code is contributed by PrinciRaj1992  

Output:

Given Linked List: 12 15 10 11 5 6 2 3 

Modified Linked List: 12 10 5 2

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

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My Personal Notes

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

C++

Java

Python3

C#

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