题目Given a non-empty, singly linked list with head node head, return a middle node of linked list.If there are two middle nodes, return the second middle node.Example 1:Input: [1,2,3,4,5]Output: Node 3 from this list (Serialization: [3,4,5])The returned node has value 3. (The judge’s serialization of this node is [3,4,5]).Note that we returned a ListNode object ans, such that:ans.val = 3, ans.next.val = 4, ans.next.next.val = 5, and ans.next.next.next = NULL.Example 2:Input: [1,2,3,4,5,6]Output: Node 4 from this list (Serialization: [4,5,6])Since the list has two middle nodes with values 3 and 4, we return the second one.Note:The number of nodes in the given list will be between 1 and 100.题目地址讲解一看到这个题目我就知道用快慢指针。但具体操作的时候有些细节需要注意，要让快慢指针指向第0个位置，而不是head（head算作第一个位置）。Java代码/** * Definition for singly-linked list. * public class ListNode { * int val; * ListNode next; * ListNode(int x) { val = x; } * } */class Solution { public ListNode middleNode(ListNode head) { System.out.println(head.val); ListNode slow = new ListNode(0); ListNode fast = new ListNode(0); slow.next = head; fast.next = head; while(slow!=null && fast!=null){ slow = slow.next; if(fast.next!=null){ fast = fast.next.next; }else{ fast = fast.next; } } return slow; }}