Delete linked list nodes which have a greater value on left side

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

Examples:

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

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

Approach:

  1. Initialize the maximum with head node.
  2. Traverse the list.
  3. Check if the next node is greater than max_node then update the value of max_node and move to the next node.
  4. Else delete the next node.

Below is the implementation of above approach:

C++

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// 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 \n");
    printList(head);
  
    delNodes(head);
  
    printf("Modified Linked List \n");
    printList(head);
  
    return 0;
}

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Java

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// Java implementation of above approach 
class GFG
{
  
// 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 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; 
        
    
    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 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); 
  
    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

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Python3

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# Python3 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
  
    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)
          
    return head
  
# 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()
    return head
  
# 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")
    printList(head)
  
    head = delNodes(head)
  
    print("Modified Linked List")
    printList(head)
  
# This code is contributed by Srathore

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C#

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// 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 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; 
        
    
    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 

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Output:

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

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