LeetCode 141. Linked List Cycle （链表循环）
Given a linked list, determine if it has a cycle in it.
Follow up:
Can you solve it without using extra space?
题目标签：Linked List
题目给了我们一个 Linked List，让我们判断它是否循环。
利用快，慢指针，快指针一次走2步，慢指针一次走1步，如果循环，快慢指针一定会相遇。
Java Solution:
Runtime beats 98.15%
完成日期：06/09/2017
关键词：singly-linked list；cycle
关键点：fast, slow pointers
1 /** 2 * Definition for singly-linked list. 3 * class ListNode { 4 * int val; 5 * ListNode next; 6 * ListNode(int x) { 7 * val = x; 8 * next = null; 9 * } 10 * } 11 */ 12 public class Solution 13 { 14 public boolean hasCycle(ListNode head) 15 { 16 if(head == null) 17 return false; 18 19 ListNode slow = head; 20 ListNode fast = head; 21 22 do 23 { 24 if(fast.next == null || fast.next.next == null) // if fast reaches to end, it doens't have a cycle 25 return false; 26 27 fast = fast.next.next; // fast moves 2 steps 28 slow = slow.next; // slow moves 1 step 29 30 31 } while(fast != slow); 32 33 return true; // if fast catches slow, meaning it has a cycle 34 } 35 }
参考资料：N/A
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