#include <stdio.h>
#include <stdlib.h>

struct node{
    int data; // data field
    struct node *next;
};

void display(struct node* head){
    struct node* current=head; // current node set to head
    
    printf("traversing the list... ");
    while(current!=NULL){ //traverse until current node isnt NULL
        printf("%d ",current->data);
        current=current->next; // go to next node        
    }    
}

struct node* reverse_N(struct node* head,struct node* temp,int n){
    struct node *next=NULL,*cur=head,*prev=temp; //initialize the pointers
    int count=0;
    while(cur!=NULL && (count++)<n){//loop till the end of linked list
        next=cur->next;//next = cur->next to store the rest of the list;
        cur->next=prev;//change the direction of linked list
        prev=cur; //update prev
        cur=next; //update cur
    }
    
    head=prev; //update head
    return head; //return head
}

struct node* creatnode(int d){
    struct node* temp=malloc(sizeof(struct node));
    temp->data=d;
    temp->next=NULL;
    return temp;
}

int main(){
    printf("creating the linked list by inserting new nodes at the end ");
    
    printf("enter 0 to stop building the list, else enter any integer ");
    
    int k,count=0,x=1,n;
    
    struct node* curr,*temp;
    
    scanf("%d",&k);
    struct node* head=creatnode(k); //buliding list, first node
    scanf("%d",&k);
    temp=head;
    ///////////////////inserting at the end//////////////////////
    while(k){
    curr=creatnode(k);
    temp->next=curr;//appending each node
    temp=temp->next;
    x++;
    scanf("%d",&k);
    }
    display(head); // displaying the list
    printf(" Input N ");
    while(1){
        scanf("%d",&n);
        if(n<x)
        break;
        printf("N greater than no of element, enter again ");
    }
    
    printf(" reversing upto first N elements... ");
    
    //traversing to the node from which no reversing needed
    temp=head;
    while((count++)<n){
        temp=temp->next;
    }
    
    head=reverse_N(head,temp,n);
    display(head); // displaying the reversed( only first N terms) list
    
    return 0;
}