Data Structure Linked List: Detect and Remove Loop in a Linked List

http://www.geeksforgeeks.org/detect-and-remove-loop-in-a-linked-list/

 #include <iostream>
 #include <vector>
 #include <algorithm>
 #include <queue>
 #include <stack>
 #include <string>
 #include <fstream>
 #include <map>
 #include <set>
 using namespace std;

 struct node {
     int data;
     node *next;
     node() : data(), next(NULL) { }
     node(int d) : data(d), next(NULL) { }
 };

 void push(node* &head, int k) {
     node *new_node = new node(k);
     new_node->next = head;
     head = new_node;
 }

 void detectandremove(node *&head) {
     node *p, *q;
     p = q = head;
     while (q && q->next) {
         q = q->next->next;
         p = p->next;
         if (p == q) break;
     }
     if (!q || !q->next) return; //no loop
     q = head;
     while (q != p) {
         q = q->next;
         p = p->next;
     } //get the starting point of the ring
     while (q->next != p) q = q->next; //get the point before the starting point of the ring
     q->next = NULL; //remove the ring
 }

 void print(node *head) {
     while (head) {
         cout << head->data << " ";
         head = head->next;
     }
 }

 int main() {
     node *head = NULL;
     push(head, );
     push(head, );
     push(head, );
     push(head, );
     push(head, );
     push(head, );
     head->next->next->next->next->next->next = head->next->next->next;
     detectandremove(head);
     print(head);
     return ;
 }