2.Add-two-numbers.java

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode node = new ListNode(0);
        ListNode current = node;
        int carry = 0;
        while(l1 != null || l2 !=null || carry != 0){
            int x = l1 != null ? l1.val : 0 ;
            int y = l2 != null ? l2.val : 0 ;
            int sum = carry + x + y ;
            carry = sum / 10 ;
            current.next = new ListNode(sum%10);
            current = current.next ;
            if (l1 != null)
                l1 = l1.next;
            if (l2 != null)
                l2 = l2.next;
        }
        return node.next ;
        
    }
}