题目：

题解：

class Solution {public boolean isPalindrome(ListNode head) {if (head == null) {return true;}// 找到前半部分链表的尾节点并反转后半部分链表ListNode firstHalfEnd = endOfFirstHalf(head);ListNode secondHalfStart = reverseList(firstHalfEnd.next);// 判断是否回文ListNode p1 = head;ListNode p2 = secondHalfStart;boolean result = true;while (result && p2 != null) {if (p1.val != p2.val) {result = false;}p1 = p1.next;p2 = p2.next;}        // 还原链表并返回结果firstHalfEnd.next = reverseList(secondHalfStart);return result;}private ListNode reverseList(ListNode head) {ListNode prev = null;ListNode curr = head;while (curr != null) {ListNode nextTemp = curr.next;curr.next = prev;prev = curr;curr = nextTemp;}return prev;}private ListNode endOfFirstHalf(ListNode head) {ListNode fast = head;ListNode slow = head;while (fast.next != null && fast.next.next != null) {fast = fast.next.next;slow = slow.next;}return slow;}
}