2. Add two numbers

1. Regular linked list

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

    // 2->4->3
    // 5->6->4
    // 7->0->8
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
    
        ListNode head,tail;
        head = tail = new ListNode(-1);
        int jw = 0;
        while(l1 != null || l2 != null || jw != 0){
    
            tail.next = new ListNode(jw);
            tail = tail.next;
            if(l1 != null){
    
                tail.val += l1.val;
                l1 = l1.next;
            }
            if(l2 != null){
    
                tail.val += l2.val;
                l2 = l2.next;
            }
            jw = tail.val / 10;
            tail.val %= 10;
        }

        return head.next;
    }

    public static void main(String[] args) {
    
        Solution solution = new Solution();
        //solution.addTwoNumbers()
    }
}