这个题，还是用我老办法。
先把链表改成数组，然后该怎么搞就怎么搞。
/**
* Definition for singly-linked list.
* function ListNode(val, next) {
* this.val = (val===undefined ? 0 : val)
* this.next = (next===undefined ? null : next)
* }
*/
/**
* @param {ListNode} head
* @return {boolean}
*/
var isPalindrome = function (head) {
const vals = [];
while (head) {
vals.push(head.val);
head = head.next;
}
let half = Math.ceil(vals.length / 2);
let is = true;
for (let i = 0; i < half; i++) {
if (vals[i] !== vals[vals.length - 1 - i]) {
is = false;
break;
}
}
return is;
};