445. Add Two Numbers II

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def addTwoNumbers(self, l1: ListNode, l2: ListNode) -> ListNode:
        s1, s2 = [], []
        while l1:
            s1.append(l1.val)
            l1 = l1.next
        while l2:
            s2.append(l2.val)
            l2 = l2.next
        carry, dummy = 0, ListNode(-1)
        while s1 or s2 or carry:
            carry += (0 if not s1 else s1.pop()) + (0 if not s2 else s2.pop())
            node = ListNode(carry % 10)
            node.next = dummy.next
            dummy.next = node
            carry //= 10
        return dummy.next

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        Deque<Integer> s1 = new ArrayDeque<>();
        Deque<Integer> s2 = new ArrayDeque<>();
        for (; l1 != null; l1 = l1.next) {
            s1.push(l1.val);
        }
        for (; l2 != null; l2 = l2.next) {
            s2.push(l2.val);
        }
        int carry = 0;
        ListNode dummy = new ListNode(-1);
        while (!s1.isEmpty() || !s2.isEmpty() || carry != 0) {
            carry += (s1.isEmpty() ? 0 : s1.pop()) + (s2.isEmpty() ? 0 : s2.pop());
            ListNode node = new ListNode(carry % 10);
            node.next = dummy.next;
            dummy.next = node;
            carry /= 10;
        }
        return dummy.next;
    }
}