class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        if (l1 == null || l2 == null) {
            return null;
        }
        List<Integer> arr1 = new ArrayList<>();
        List<Integer> arr2 = new ArrayList<>();
        while (l1 != null) {
            arr1.add(l1.val);
            l1 = l1.next;
        }

        while (l2 != null) {
            arr2.add(l2.val);
            l2 = l2.next;
        }

        List<Integer> res = addTwoNumbers(arr1, arr2);

        ListNode p = new ListNode(res.get(0));
        ListNode t = p;
        for (int i = 1; i < res.size(); i++) {
            t.next = new ListNode(res.get(i));
            t = t.next;
        }
        return p;
    }

    public List<Integer> addTwoNumbers(List<Integer> arr1, List<Integer> arr2) {
        int m = arr1.size();
        int n = arr2.size();
        int left = m - 1;
        int right = n - 1;
        int d = 0;
        List<Integer> res = new ArrayList();
        while (left >= 0 && right >= 0) {

            int v = d + arr1.get(left) + arr2.get(right);
            int s = v % 10;
            res.add(s);
            d = v / 10;
            left--;
            right--;
        }

        while (left >= 0) {
            int v = d + arr1.get(left);
            int s = v % 10;
            res.add(s);
            d = v / 10;
            left--;
        }

        while (right >= 0) {
            int v = d + arr2.get(right);
            int s = v % 10;
            res.add(s);
            d = v / 10;
            right--;
        }

        if (d > 0) {
            res.add(d);
        }

        List<Integer> res2 = new ArrayList();

        for (int i = res.size() - 1; i >= 0; i--) {
            res2.add(res.get(i));
        }
        return res2;
    }

}