Given a linked list, determine if it has a cycle in it.
题意：给你一个链表，找出是否它的内部有环形的圆。
思路：来两个指针，一个一次走一步，一个一次走两步，如果第二个能追上第一个就代表有圆。
java代码：
/**
* Definition for singly-linked list.
* class ListNode {
* int val;
* ListNode next;
* ListNode(int x) {
* val = x;
* next = null;
* }
* }
*/
public class Solution {
public boolean hasCycle(ListNode head) {
if (head == null)
return false;
ListNode slow = head;
ListNode fast = head;
while (fast.next != null && fast.next.next != null) {
slow = slow.next;
fast = fast.next.next;
if (slow == fast)
return true;
}
return false;
}
}
