leetcode 141. 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?

题意：

判断一个链表是否有环。

解决方案：

双指针，快指针每次走两步，慢指针每次走一步，

如果有环，快指针和慢指针会在环内相遇，fast == slow，这时候返回true。

如果没有环，返回false.

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

转载于:https://www.cnblogs.com/iwangzheng/p/5695174.html

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