Palindrome Linked List

Reverse Second Half

function isPalindrome(head) {
  let slow = head, fast = head;
  while (fast && fast.next) { slow = slow.next; fast = fast.next.next; }
  let prev = null;
  while (slow) { const next = slow.next; slow.next = prev; prev = slow; slow = next; }
  while (prev) {
    if (prev.val !== head.val) return false;
    prev = prev.next; head = head.next;
  }
  return true;
}

Time: O(n) | Space: O(1)