103. Linked List Cycle II

ListNode * detectCycle(ListNode * head) { // write your code here if(head == NULL){ return head; } ListNode *slow = head; ListNode *fast = head; while(fast != NULL && fast->next != NULL){ slow = slow->next; fast = fast->next->next; if(slow == fast){ break; } } if(fast == NULL || fast->next == NULL){ return NULL; } while(head != slow){ head = head->next; slow = slow->next; } return head; }