LeetCode——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?

原题链接：https://oj.leetcode.com/problems/linked-list-cycle/

题目：给定一个链表，判断它是否有环。

继续：

你能不用额外的空间解决吗？

思路：使用两个指针fast,slow，fast每次向前走两步，slow每次向前走一步，如果二者对应的节点相等，即存在环。

public boolean hasCycle(ListNode head) {ListNode fast = head,slow = head;if(head == null || head.next == null)return false;while(fast != null && fast.next != null){slow = slow.next;fast = fast.next.next;if(slow == fast)return true;}return false; }// Definition for singly-linked list.class ListNode {int val;ListNode next;ListNode(int x) {val = x;next = null;}}