Given the head of a singly linked list, return true if it is a palindrome or false otherwise.
Example 1:
Input: head = [1,2,2,1] Output: true Example 2:
Input: head = [1,2] Output: false
Constraints:
The number of nodes in the list is in the range [1, 105]. 0 <= Node.val <= 9
Follow up: Could you do it in O(n) time and O(1) space?