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

// T: O(max(|l1|, |l2|))

// S: O(max(|l1|, |l2|))

public class AddTwoNumbers {

public ListNode addTwoNumbers(ListNode l1, ListNode l2) {

ListNode result = new ListNode();

ListNode current = result;

int carry = 0;

while (l1 != null || l2 != null) {

current.next = new ListNode();

current = current.next;

int sum = get(l1) + get(l2) + carry;

current.val = sum % 10;

carry = sum / 10;

l1 = next(l1);

l2 = next(l2);

}

if (carry > 0) {

current.next = new ListNode(carry);

}

return result.next;

}

private ListNode next(ListNode node) {

if (node == null) return null;

return node.next;

}

private int get(ListNode node) {

if (node == null) return 0;

return node.val;

}

}