linkedlist_reverse.cpp

#include<bits/stdc++.h>
using namespace std;
class node{
    public:
    int data;
    node* next;
    node(int val){
        data=val;
        next=NULL;
    }
};
void insertAthead(node* &head, int val){
    node* n=new node(val);
    n->next=head;
    head=n;
}
void insterAttail(node* &head, int val){
    node* n=new node(val);
    if(head==NULL){
        head=n;
        return;
    }
    node* temp=head;
    while(temp->next!=NULL){
        temp=temp->next;
    }
    temp->next=n;
}
void print(node* head){
    node* teamp=head;
    while(teamp!=NULL){
        cout<<teamp->data<<"->";
        teamp=teamp->next;
    }
    cout<<"NULL"<<endl;
}
node* reverse(node* &head){
    node* prev=NULL;
    node* curr=head;
    node* next;
    while(curr!=NULL){
        next=curr->next;
        curr->next=prev;
        prev=curr;
        curr=next;
    }
    return prev;
}
node* reversek(node* &head, int k){
    node* prev=NULL;
    node* curr=head;
    node* next;
    int count=0;
    while(curr!=NULL && count<k){
        next=curr->next;
        curr->next=prev;
        prev=curr;
        curr=next;
        count++;
    }
    if(next!=NULL){
        head->next=reversek(next, k);
    }
    return prev;
}
int main(){
    node* head=NULL;
    insterAttail(head, 1);
    insterAttail(head, 2);
    insterAttail(head, 3);
    insertAthead(head, 4);
    print(head);
    node* newhead=reverse(head);
    print(newhead);
    node* newh=reversek(newhead, 2);
    print(newh);
}