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Delete all the nodes from the list that are greater than x

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  • Difficulty Level : Easy
  • Last Updated : 05 Jul, 2022

Given a linked list, the problem is to delete all the nodes from the list that are greater than the specified value x. Examples:

Input : list: 7->3->4->8->5->1
        x = 6
Output : 3->4->5->1

Input : list: 1->8->7->3->7->10
        x = 7
Output : 1->7->3->7

Source: Microsoft Interview Experience | Set 169.

Approach: This is mainly a variation of the post which deletes first occurrence of a given key. We need to first check for all occurrences at head node which are greater than ‘x’, delete them and change the head node appropriately. Then we need to check for all occurrences inside a loop and delete them one by one. 

CPP




// C++ implementation to delete all the nodes from the list
// that are greater than the specified value x
#include <bits/stdc++.h>
   
using namespace std;
   
// structure of a node
struct Node {
    int data;
    Node* next;
};
   
// function to get a new node
Node* getNode(int data)
{
    Node* newNode = new Node;
    newNode->data = data;
    newNode->next = NULL;
    return newNode;
}
   
// function to delete all the nodes from the list
// that are greater than the specified value x
void deleteGreaterNodes(Node** head_ref, int x)
{
    Node *temp = *head_ref, *prev;
   
    // If head node itself holds the value greater than 'x'
    if (temp != NULL && temp->data > x) {
        *head_ref = temp->next; // Changed head
        free(temp); // free old head
        temp = *head_ref; // Change temp
    }
   
    // Delete occurrences other than head
    while (temp != NULL) {
   
        // Search for the node to be deleted,
        // keep track of the previous node as we
        // need to change 'prev->next'
        while (temp != NULL && temp->data <= x) {
            prev = temp;
            temp = temp->next;
        }
   
        // If required value node was not present
        // in linked list
        if (temp == NULL)
            return;
   
        // Unlink the node from linked list
        prev->next = temp->next;
   
        delete temp; // Free memory
   
        // Update Temp for next iteration of
        // outer loop
        temp = prev->next;
    }
}
   
// function to a print a linked list
void printList(Node* head)
{
    while (head) {
        cout << head->data << " ";
        head = head->next;
    }
}
   
// Driver program to test above
int main()
{
    // Create list: 7->3->4->8->5->1
    Node* head = getNode(7);
    head->next = getNode(3);
    head->next->next = getNode(4);
    head->next->next->next = getNode(8);
    head->next->next->next->next = getNode(5);
    head->next->next->next->next->next = getNode(1);
   
    int x = 6;
   
    cout << "Original List: ";
    printList(head);
   
    deleteGreaterNodes(&head, x);
   
    cout << "\nModified List: ";
    printList(head);
   
    return 0;
}

Java




// Java implementation to delete all nodes from the list
// that are greater than the specified value x
import java.io.*;
 
class Node {
    int data;
    Node next;
}
 
class GFG {
 
    // Function to get a new node.
    public Node getNode(int data)
    {
        Node new_node = new Node();
        new_node.data = data;
        new_node.next = null;
        return new_node;
    }
 
    // Function to print linked list.
    public void printList(Node head)
    {
        Node temp = head;
        while (temp != null) {
            System.out.print(temp.data + " ");
            temp = temp.next;
        }
    }
 
    // Functions to delete nodes which have greater value
    // than x.
    public Node deleteGreaterNodes(Node head, int x)
    {
        Node temp = head;
       
        // while loop takes care if head node value greater
        // than x.
        while (temp != null && temp.data > x) {
            temp = temp.next;
            head = temp; // new head.
        }
        temp = head;
        Node prev = temp;
       
        // nodes other than head having value greater than x
        while (temp != null) {
            while (temp != null && temp.data <= x) {
                prev = temp;
                temp = temp.next;
            }
            if (temp == null) {
                return head;
            }
            // if there is a node in middle which has
            // greater value, we point the node to the next
            // node.
            prev.next = temp.next;
            // update temp for next iteration of loop.
            temp = prev.next;
        }
        return head;
    }
 
    public static void main(String[] args)
    {
 
        GFG list = new GFG();
 
        // Create list: 7->3->4->8->5->1.
        Node head = list.getNode(7);
        head.next = list.getNode(3);
        head.next.next = list.getNode(4);
        head.next.next.next = list.getNode(8);
        head.next.next.next.next = list.getNode(5);
        head.next.next.next.next.next = list.getNode(1);
 
        System.out.print("Original List: ");
        list.printList(head);
 
        int x = 6;
 
        head = list.deleteGreaterNodes(head, x);
        System.out.print("\nModified List: ");
        list.printList(head);
    }
}
 
// This code is contributed by lokesh (lokeshmvs21).

Output:

Original List: 7 3 4 8 5 1 
Modified List: 3 4 5 1

Time Complexity: O(n).


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