C++ Program To Delete Nodes Which Have A Greater Value On Right Side

// C++ program to delete nodes which 
// have a greater value on right side
#include <bits/stdc++.h>
using namespace std;

// Structure of a linked list node 
struct Node
{
    int data;
    struct Node* next;
};

// Prototype for utility functions 
void reverseList(struct Node** headref);
void _delLesserNodes(struct Node* head);

/* Deletes nodes which have a node with 
   greater value node on left side */
void delLesserNodes(struct Node** head_ref)
{
    // 1. Reverse the linked list 
    reverseList(head_ref);

    /* 2. In the reversed list, delete nodes 
          which have a node with greater value 
          node on left side. Note that head node 
          is never deleted because it is the 
          leftmost node.*/
    _delLesserNodes(*head_ref);

    /* 3. Reverse the linked list again to 
          retain the original order */
    reverseList(head_ref);
}

/* Deletes nodes which have
   greater value node(s) on left side */
void _delLesserNodes(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 smaller than max,
           then delete current */
        if (current->next->data < 
            maxnode->data) 
        {
            temp = current->next;
            current->next = temp->next;
            free(temp);
        }

        /* If current is greater than max, 
           then update max and move current */
        else
        {
            current = current->next;
            maxnode = current;
        }
    }
}

/* Utility function to insert a node 
   at the beginning */
void push(struct Node** head_ref, 
          int new_data)
{
    struct Node* new_node = 
           (struct Node*)malloc(sizeof(struct Node));
    new_node->data = new_data;
    new_node->next = *head_ref;
    *head_ref = new_node;
}

/* Utility function to reverse a 
   linked list */
void reverseList(struct Node** headref)
{
    struct Node* current = *headref;
    struct Node* prev = NULL;
    struct Node* next;
    while (current != NULL) 
    {
        next = current->next;
        current->next = prev;
        prev = current;
        current = next;
    }
    *headref = prev;
}

/* Utility function to print a 
   linked list */
void printList(struct Node* head)
{
    while (head != NULL) 
    {
        cout << " " << head->data ;
        head = head->next;
    }
    cout << "" ;
}

// Driver code
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);

    cout << "Given Linked List " ;
    printList(head);

    delLesserNodes(&head);

    cout << "Modified Linked List " ;
    printList(head);

    return 0;
}
// This code is contributed by shivanisinghss2110