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Question:
Given a linked list, determine if it has a cycle in it.
Follow up:
Can you solve it without using extra space?
Analysis:
思路一：快慢指针法。前面用到过快慢指针寻找链表的中间节点。若快慢指针会相遇，则说明有环；否则快指针遇到null，则说明无环。
Answer：（Beats 100% java submission~）
public class Solution { public boolean hasCycle(ListNode head) { if(head == null) return false; ListNode fast = head, slow = head; while(fast.next != null || fast == null) { if(fast.next == null || fast == null || fast.next.next == null) return false; slow = slow.next; fast = fast.next.next; if(slow == fast) return true; } return false; } }
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原文地址：http://www.cnblogs.com/little-YTMM/p/4803579.html
