Create a function expand, which takes in a pointer to the head of the linked list, and returns a pointer to the head of a linked list in which all strings repeat following the rules described above.

Example:

"apple"->NULL

return "apple"->"apple"->NULL

"green"->"green"->"blue"->"red"->"green"->NULL

return "green"->"green"->"blue"->"blue"->"red"->"red"->"green"->"green"->NULL

The linked lists for this problem use the following class declaration:

class node {

public: string data;

node* next;

};

Do this in C++. Code in bold CANNOT be changed:

node* expand(node* head) {

while(head != NULL) {

head->data = head->data+head->next;

head = head->next;

}

}