2. Add Two Numbers

/**
 * 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 result = new ListNode(0);
        ListNode ptr = result;
        int carry=0;
        while(l1!=null || l2!=null){
            int sum =carry;
            if(l1!=null){
                sum = sum +l1.val;
                l1 = l1.next;
            }
            if(l2!=null){
                sum = sum+l2.val;
                l2 = l2.next;
            }
         
            carry =sum/10;
             sum =sum%10;
              
            ptr.next = new ListNode(sum);
            ptr = ptr.next;
        }
//         if carry remain in last
        if(carry==1) ptr.next = new ListNode(1);
        return result.next;
    }
}