s0002_add_two_numbers

2. Add Two Numbers

Medium

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

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Example 1:

Input: l1 = [2,4,3], l2 = [5,6,4]

Output: [7,0,8]

Explanation: 342 + 465 = 807.

Example 2:

Input: l1 = [0], l2 = [0]

Output: [0]

Example 3:

Input: l1 = [9,9,9,9,9,9,9], l2 = [9,9,9,9]

Output: [8,9,9,9,0,0,0,1]

Constraints:

• The number of nodes in each linked list is in the range [1, 100].
• 0 <= Node.val <= 9
• It is guaranteed that the list represents a number that does not have leading zeros.

Solution

require_relative '../../com_github_leetcode/list_node'

# Definition for singly-linked list.
# class ListNode
#     attr_accessor :val, :next
#     def initialize(val = 0, _next = nil)
#         @val = val
#         @next = _next
#     end
# end
# @param {ListNode} l1
# @param {ListNode} l2
# @return {ListNode}
def add_two_numbers(l1, l2)
  dummy_head = ListNode.new(0)
  p = l1
  q = l2
  curr = dummy_head
  carry = 0

  while p || q
    x = p ? p.val : 0
    y = q ? q.val : 0
    sum = carry + x + y
    carry = sum / 10
    curr.next = ListNode.new(sum % 10)
    curr = curr.next

    p = p.next if p
    q = q.next if q
  end

  curr.next = ListNode.new(carry) if carry > 0

  dummy_head.next
end