[LeetCode]No.141 Linked List Cycle

链接:https://leetcode.com/problems/linked-list-cycle/
原题:
Given a linked list, determine if it has a cycle in it.

Follow up:
Can you solve it without using extra space?

分析：这道题的意思是在不开辟另外内存空间的情况下 判断是否是循环的链表
这里用两个游标用来做比较，一个是一个跳两个节点，一个是一次跳一个节点，如果是循环链表，两个游标肯定有重合的时候

/**
 * 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) {
         ListNode fast = head;
        ListNode slow = head;
        while (true) {
            if(fast == null || slow== null) {
                return false;
            }
            fast = fast.next;
            if(slow.next!=null) {
               slow = slow.next.next;
            } else {
                return false;
            }
            if(fast == slow) {
                return true;
            }
        }
    }
}