LeetCode 2. Add Two Numbers

Question

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.

https://leetcode.com/problems/add-two-numbers/

• Solution1

class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        int carry = 0;
        ListNode dummy = new ListNode(-1), cur = dummy;
        while(l1!=null || l2 != null){
            int sum = carry;
            if(l1 != null){
                sum += l1.val;
                l1 = l1.next;
            }
            if(l2 != null){
                sum += l2.val;
                l2 = l2.next;
            }
            cur.next = new ListNode(sum % 10);
            cur = cur.next;
            carry = sum / 10;
        }
        if (carry > 0) cur.next = new ListNode(carry);
        return dummy.next;
    }
}

Complexity:

Time complexity: O(n)

Space complexity: O(n)