141. Linked List Cycle
Given a linked list, determine if it has a cycle in it.
Follow up:
Can you solve it without using extra space?
判断一个链表是否有环
C++(10ms):
1 /** 2 * Definition for singly-linked list. 3 * struct ListNode { 4 * int val; 5 * ListNode *next; 6 * ListNode(int x) : val(x), next(NULL) {} 7 * }; 8 */ 9 class Solution { 10 public: 11 bool hasCycle(ListNode *head) { 12 if (head == NULL) 13 return false ; 14 ListNode* runner = head ; 15 ListNode* walker = head ; 16 while(runner->next != NULL && runner->next->next != NULL ){ 17 walker = walker->next ; 18 runner = runner->next->next ; 19 if (runner == walker) 20 return true ; 21 } 22 return false ; 23 } 24 };