Implement the following function as a new function for the linked list toolkit. (Use the usual node definition with member variables called data and link.)

bool is_on(const node* head_ptr, const node* p);

// Precondition: head_ptr is the head pointer of a linked list (which might be empty, or might be non-empty).

//The pointer p is a non-NULL pointer to some node on some linked list.

// Postcondition: The return value is true if p actually points to

// one of the nodes in the head_ptr's linked list. For example,

// p might point to the head node of this list, or the second node,

// or the third node, and so on. Otherwise the return value is

// false. None of the nodes on any lists are changed.