141. Linked List Cycle.cpp

class Solution {
public:
   bool hasCycle(ListNode *head) {
      ListNode* slow=head;
      ListNode* fast=head;
        while(fast && slow && fast->next){
            slow=slow->next;
            fast=fast->next->next;
            if(fast==slow)
               return true;
        }
        return false;
    }
};