GFG_Linked_List_Reverse_Alter_K.cpp

#include <iostream>
#include<bits/stdc++.h>
typedef long long ll;
using namespace std;
struct node{
    ll data;
    struct node *next;
};

struct node* insert_head(struct node* head, ll value)
{
    struct node* new_node=(struct node*)(malloc(sizeof(struct node)));
    new_node->data=value;
    new_node->next=head;
    head=new_node;
    return head;
    
}
struct node* insert_tail(struct node* head,ll value)
{
    struct node* new_node=(struct node*)(malloc(sizeof(struct node)));
    new_node->data=value;
    new_node->next=NULL;
    struct node* temp_point=head;
    while(temp_point->next!=NULL)
        temp_point=temp_point->next;
    temp_point->next=new_node;
    return head;
    
}
void display(struct node* head)
{
    struct node* temp_head=head;
    cout<<"Linked List is "<<endl;
    while(temp_head!=NULL)
    {
        cout<<temp_head->data<<" ";
        temp_head=temp_head->next;
    }
    cout<<endl;
}
struct node* reverse_Alter_K(struct node* head, ll k)
{
    struct node* curr=head;
    struct node* nextn=NULL;
    struct node* prev=NULL;
    struct node* last=NULL;
    ll count=1;
    while(curr!=NULL && count<=2*k)
    {
        last=curr;
        if(count<=k)
        {
            nextn=curr->next;
            curr->next=prev;
            prev=curr;
            curr=nextn;
        }
        else if(count==k+1)
        {
            nextn=curr->next;
            head->next=curr;
            curr=curr->next;
        }
        else
            {
                nextn=curr->next;
                curr=curr->next;
            }
            
        count++;
    }
    
    if(curr!=NULL)
       last->next=reverse_Alter_K(nextn,k);
     return prev;
       
    
    
}

int main() {
    
    struct node *head=NULL;
    head=insert_head(head,100);
    head=insert_head(head,90);
    head=insert_head(head,70);
    head=insert_head(head,60);
    head=insert_head(head,50);
    head=insert_head(head,40);
    head=insert_head(head,30);
    head=insert_head(head,20);
    display(head);
    head=reverse_Alter_K(head,3);
    display(head);
    
}