Poison

445. Add Two Numbers II

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class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode dummyHead = new ListNode();

        Stack<Integer> stackA = new Stack<>();
        Stack<Integer> stackB = new Stack<>();

        while (l1 != null) {
            stackA.push(l1.val);
            l1 = l1.next;
        }
        while (l2 != null) {
            stackB.push(l2.val);
            l2 = l2.next;
        }

        int carry = 0;
        while (!stackA.isEmpty() || !stackB.isEmpty() || carry != 0) {
            int sum = carry;
            if (!stackA.isEmpty()) {
                sum += stackA.pop();
            }
            if (!stackB.isEmpty()) {
                sum += stackB.pop();
            }

            ListNode next = dummyHead.next;
            dummyHead.next = new ListNode(sum % 10);
            dummyHead.next.next = next;
            carry = sum / 10;
        }

        return dummyHead.next;
    }
}
Reference

445. Add Two Numbers II
剑指 Offer II 025. 链表中的两数相加