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

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  • Difficulty Level : Medium
  • Last Updated : 02 Sep, 2022
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Given a singly linked list, the task is to remove all the nodes which have a greater value on the 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.

Implementation:

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

Java




// 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

Python3




# 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

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 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

Javascript




<script>
 
// JavaScript implementation of above approach
 
// Structure of a linked list node
class Node {
    constructor(val) {
        this.data = val;
        this.next = null;
    }
}
 
    // Function to Delete nodes which have
    // greater value node(s) on right side
    function delNodes(head) {
var current = head;
 
        // Initialize max
var maxnode = head;
var 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
    function push(head_ref , new_data) {
     var 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 /
    function printList(head) {
        while (head != null) {
            document.write(head.data + " ");
            head = head.next;
        }
        document.write();
        return head;
    }
 
    // Driver code
     
     var 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);
 
        document.write("Given Linked List <br/>");
        printList(head);
 
        head = delNodes(head);
 
        document.write("<br/>Modified Linked List <br/>");
        printList(head);
 
// This code contributed by umadevi9616
 
</script>

Output

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

Complexity Analysis:

  • Time Complexity: O(N), for traversing over the linked list the overall time complexity is linear.
  • Auxiliary Space: O(1) because no extra space is required.

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