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。推断它是否有环。
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。假设二者相应的节点相等。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; } }