# Definition for singly-linked list.

class ListNode

attr_accessor :val, :next

def initialize(val)

@val = val

@next = nil

end

end

# @param {ListNode} head

# @return {Boolean}

def is_palindrome(head)

if head.nil? or head.next.nil?

return true

end

value_array = Array.new

ptr = head

until ptr.nil?

value_array << ptr.val

ptr = ptr.next

end

left = 0; right = value_array.size - 1

while left < right

if value_array[left] != value_array[right]

return false

end

left += 1; right -= 1

end

true

end

head = ListNode.new 1

head.next = ListNode.new 2

head.next.next = ListNode.new 1

puts is_palindrome head