141. Linked List Cycle【easy】
Given a linked list, determine if it has a cycle in it.
Follow up:
Can you solve it without using extra space?
解法一:
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 || head->next == NULL) { 13 return false; 14 } 15 16 ListNode * slow = head; 17 ListNode * fast = head; 18 19 while (fast->next != NULL && fast->next->next != NULL) { 20 slow = slow->next; 21 fast = fast->next->next; 22 23 if (fast == slow) { 24 return true; 25 } 26 } 27 28 return false; 29 } 30 };
经典的快慢指针思想