EvenafterOdd.cpp

#include <iostream>
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 insertAtTail(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 display(node* head){
    node* temp = head;
    while(temp != NULL){
        cout << temp->data << "->";
        temp=temp->next;
    }
    cout << "NULL\n";
}

void evenaferOdd(node* &head){
    node* odd= head;
    node* even = head->next;
    node* evenStart = even;
    while(odd->next!=NULL && even -> next!=NULL){
        odd->next = even->next;
        odd = odd->next;
        even->next = odd->next;
        even=even->next;
    }
    odd->next = evenStart;
    if(odd->next!=NULL){
        even->next =NULL;
    }
}

int main(){
    node* head= NULL;
    int arr[] = {1,2,3,4,5,6};
    for(int i=0; i<6; i++){
        insertAtTail(head,arr[i]);
    }
    display(head);

    evenaferOdd(head);
    display(head);




    return 0;
}