var reverseList = function(head2) {
    let p1 = head2;
    let p2 = null;
    while(p1) {
        const temp = p1.next;
        p1.next = p2;
        p2 = p1;
        p1 = temp;
    }
    return p2;
};
var isPalindrome = function(head) {
    let head2 = reverseList(head);
    while(head && head2) {
        if (head.val !== head2.val) return false;
    }
    return true
};