标签：style blog io color for sp div on log
Given a linked list, determine if it has a cycle in it.
Follow up:
Can you solve it without using extra space?
思路：快慢指针的应用。快慢指针指的是移动的步长，即每次向前移动的快慢。例如可以让快指针每次沿链表向前移动2，慢指针每次向前移动1次。
如果快指针到达NULL,说明链表以NULL为结尾，没有环。如果快指针追上慢指针，则表示有环。
时间复杂度O(n),空间复杂度O(1)
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) return head; 13 14 ListNode *slow = head, *fast = head; 15 while (fast != NULL && fast->next != NULL) { 16 fast = fast->next->next; 17 slow = slow->next; 18 if (fast == slow) return true; 19 } 20 21 return false; 22 } 23 };
标签：style blog io color for sp div on log
原文地址：http://www.cnblogs.com/vincently/p/4072091.html
