leetcode142.环形链表II

思路源自代码随想录，通过快慢指针解决

/*** Definition for singly-linked list.* class ListNode {*     int val;*     ListNode next;*     ListNode(int x) {*         val = x;*         next = null;*     }* }*/
public class Solution {public ListNode detectCycle(ListNode head) {ListNode slow = head;ListNode fast = head;while (fast != null && fast.next != null) {slow = slow.next;fast = fast.next.next;if (slow == fast) {ListNode index1 = head;ListNode index2 = fast;while (index1 != index2) {index1 = index1.next;index2 = index2.next;}return index1;}}return null;}
}