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   

Approach:

1. Initialise a variable maximum with head node.
2. Traverse the list.
3. Check if the next node is lesser than max_node. If yes, move to the next node.
4. 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

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 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 /
    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 program to test above functions /

       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 ");
        printList(head);

        head = delNodes(head);

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

// This code contributed by umadevi9616

</script>

Output:

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

Modified Linked List: 12 10 5 2

Time Complexity: O(N), since one traversal of the linked List is required to complete all operations hence the overall time required by the algorithm is linear
Auxiliary Space: O(1) , since no extra array is used the space taken by the algorithm is constant