/**

  • Definition for singly-linked list.
  • struct ListNode {
  • int val;

  • ListNode *next;

  • ListNode(int x) : val(x), next(NULL) {}
  • }; */ class Solution { public: bool hasCycle(ListNode *head) { if(!head) return false; auto slow = head; auto fast = head; while(slow -> next && fast -> next && fast -> next -> next) { slow = slow -> next; fast = fast -> next -> next; if(slow == fast) { return true; } } return false; } };