标签：div turn logs contain hash contains etc boolean als
Given a linked list, determine if it has a cycle in it.
Follow up:
Can you solve it without using extra space?
这道题很简单也很经典感觉。一开始用hashset做的，但这样就用了extra space了。后来发现可以用双指针。
hashset
public class Solution { public boolean hasCycle(ListNode head) { if (head == null) { return false; } Set<ListNode> hs = new HashSet<>(); while (true) { if (head == null) { return false; } if (hs.contains(head)) { break; } hs.add(head); head = head.next; } return true; } }
双指针
public class Solution { public boolean hasCycle(ListNode head) { if (head == null) { return false; } ListNode fast = head; ListNode slow = head; while (fast.next != null) { fast = fast.next.next; slow = slow.next; if (fast == slow) { return true; } if (fast == null) { break; } } return false; } }
双指针是公认的解法，这次都忘记了，下次要记住。。。
标签：div turn logs contain hash contains etc boolean als
原文地址：http://www.cnblogs.com/aprilyang/p/6305823.html
