detect loop (I've seen this one before)

detect_loop.cxx

class Node 
{
public:
    Node() : next(NULL), value(0) {}
    Node(int v) : next(NULL), value(v){}
    Node* next;
    int value;
};

bool detect_loop(Node* head)
{
    Node *n1, *n2;
    n1 = n2 = head;
    while (n1->next != NULL && n2->next != NULL)
    {
        n1 = n1->next;
        n2 = n2->next;
        if (n2->next != NULL)
             n2 = n2->next;
        if (n1 == n2) return true;
    }
    return false;
}

int main()
{
    // Make a list with a loop in it.
    int n = 10;
    Node* head = new Node(0);
    Node* curr = head;
    
    for (int i = 1; i < n; i++)
    {
        Node* t = new Node(i);
        curr->next = t;
        curr = t;
    }
    // LOOP! (comment out to make regular)
    curr->next = head;
    
    bool loop = detect_loop(head);
    std::cout << "There is a loop: " << loop << std::endl;
    return 1;
}