LeetCode 2 Add Two Numbers

You are given two linked lists representing two non-negative numbers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8

# Definition for singly-linked list.
# class ListNode
#     attr_accessor :val, :next
#     def initialize(val)
#         @val = val
#         @next = nil
#     end
# end

# @param {ListNode} l1
# @param {ListNode} l2
# @return {ListNode}
def add_two_numbers(l1, l2)
    return l1 if l2.nil?

    return l2 if l1.nil?

    s1 = Array.new
    s2 = Array.new
    n = Array.new
    while l1
        s1.unshift(l1.val)
        l1 = l1.next
    end
    while l2
        s2.unshift(l2.val)
        l2 = l2.next
    end
    x = s1.join.to_i+s2.join.to_i
    n = x.to_s.chars.map(&:to_i)
    
    ans = ListNode.new(0)
    d = ans
    l = n.length()
    l.times do
        d.next = ListNode.new(n.pop)
        d = d.next
    end
    ans.next
end