【easy】141. Linked List Cycle

很是簡單的題：判斷鏈表有沒有環（用快慢指針）

/** * 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 == NULL) return false; ListNode *fast = head; ListNode *slow = head; while (fast->next != NULL){ fast = fast->next->next; slow = slow->next; if (fast == NULL) return false; if (fast == slow) return true; } return false; } };