Solution.js

var isPalindrome2 = function (head) {
  if (!head || !head.next) {
    return true;
  }
  let slow = head;
  let fast = head;
  while (fast !== null && fast.next !== null) {
    slow = slow.next;
    fast = fast.next.next;
  }
  if (fast !== null) {
    slow = slow.next;
  }

  let p = new ListNode(0);
  while (slow !== null) {
    let t = slow.next;
    slow.next = p.next;
    p.next = slow;
    slow = t;
  }

  let left = head;
  let right = p.next;
  while (right !== null) {
    if (left.val !== right.val) {
      return false;
    }
    left = left.next;
    right = right.next;
  }
  return true;
};

var isPalindrom3 = function (head) {
  let arr = [];
  let next = head;
  while (next) {
    arr.push(next.val);
    next = next.next;
  }
  let len = Math.trunc(arr.length / 2);
  for (let i = 0; i < len; i++) {
    if (arr[i] !== arr[arr.length - 1 - i]) {
      return false;
    }
  }
  return true;
};

var isPalindrome = function (head) {
  let arr = [];
  while (head) {
    arr.push(head.val);
    head = head.next;
  }
  return arr.join("") === arr.reverse().join("");
};