Palindrome Linked List

Return True if the list reads the same forwards and backwards. Try to use only O(1) extra memory (copying the values into a Python list is the easy way, but the challenge is to do it with pointers).

The tests show a list as a Python list of its values: [1, 2, 3] stands for 1 -> 2 -> 3.

Examples

Example 1

Input:

is_palindrome_list(head)  # head = 1 -> 2 -> 2 -> 1

Output:

True

Example 2

Input:

is_palindrome_list(head)  # head = 1 -> 2

Output:

False

Constraints

• 0 <= number of nodes <= 100000
• 0 <= val <= 9