Reverse doubly linked list (recursive)

#include <iostream>

using namespace std;

class node {

public:

    int val;

    node *next;

    node *prev;

    node(int val_) {

        val = val_;

        next = NULL;

        prev = NULL;

    }

};

void print(node *head) {

    while (head != NULL) {

        cout << head -> val << "<=>";

        head = head -> next;

    }

    cout << endl;

}

node * create() {

    node *head = NULL;

    node *iter = head;

    for (int i = 1; i <= 6; i++) {

        if (i == 1) {

            head = new node(i);

            iter = head;

        } else {

            iter -> next = new node(i);

            iter -> next -> prev = iter;

            iter = iter -> next;

        }

    }

    return head;

}

// NULL<-1<->2<->3<->4<->5<->6->NULL

// 1 -> right = 2            // 1 -> right = NULL

// 1 -> left = NULL          // 1 -> left = 2

// 2 -> left = 1             // 2 -> right = 1

// 2 -> right = NULL         // 2 -> left = NULL

// 1 2 3 4 5 6

// 6 5 4 3 2 1

node *reverse(node* head, node*& new_head) {

    if (head == NULL || head -> next == NULL) {

        if (new_head == NULL) {

            new_head = head;

        }

        return head;

    }

    

    node* returned_node = reverse(head -> next, new_head);

    returned_node -> next = head;

    head -> prev = returned_node;

    return head;

}

int main()

{

    node *head = create();

    print(head);

    

    node *new_head = NULL;

    node *head_ret = reverse(head, new_head);

    new_head -> prev = NULL;

    head_ret -> next = NULL;

    print(new_head);

    

    return 0;

}