function ListNode(val, next) {this.val = val === undefined ? 0 : val;this.next = next === undefined ? null : next;
}var isPalindrome = function (head) {if (!head || !head.next) {return true; }// 使用快慢指针法找到链表的中间节点let slow = head;let fast = head;while (fast && fast.next) {slow = slow.next;fast = fast.next.next;}// 翻转链表的后半部分let prev = null;while (slow) {let temp = slow.next;slow.next = prev;prev = slow;slow = temp;}let left = head;let right = prev;while (right) {if (left.val !== right.val) {return false; }left = left.next;right = right.next;}return true;
};