// https://leetcode.com/problems/add-two-numbers
class Solution {

    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        BigInteger sumOfParsedNumbers = getReverseNumber(l1).add(getReverseNumber(l2));

        ListNode newListNode = new ListNode();
        ListNode currentlyReadingNode = newListNode;

        char[] chars = String.valueOf(sumOfParsedNumbers).toCharArray();

        for (int i = chars.length - 1; i >= 0; i--) {
            currentlyReadingNode.val = Integer.parseInt(String.valueOf(chars[i]));

            if (i > 0) {
                currentlyReadingNode.next = new ListNode();
                currentlyReadingNode = currentlyReadingNode.next;
            }

        }

        return newListNode;
    }

    public BigInteger getReverseNumber(ListNode listNode) {
        StringBuilder stringifiedNumber = new StringBuilder();

        while (true) {
            stringifiedNumber.append(listNode.val);

            if (listNode.next != null) {
                listNode = listNode.next;
            } else {
                break;
            }
        }

        return new BigInteger(stringifiedNumber.reverse().toString());
    }
}

class ListNode {

    int val;
    ListNode next;

    ListNode() {
    }

    ListNode(int val) {
        this.val = val;
    }

    ListNode(int val, ListNode next) {
        this.val = val;
        this.next = next;
    }
}