Add Two Numbers

public class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        if(l1 == null)
            return l2;
        if(l2 == null)
            return l1;
        ListNode fakehead = new ListNode(0);
        ListNode pre = fakehead;
        int carry = 0;
        ListNode runner1 = l1;
        ListNode runner2 = l2;
        while(runner1 != null && runner2 != null){
            int tmp = runner1.val + runner2.val + carry;
            carry = tmp / 10;
            ListNode newnode = new ListNode(tmp%10);
            pre.next = newnode;
            pre = newnode;
            runner1 = runner1.next;
            runner2 = runner2.next;
        }
        while(runner1 != null ){
            int tmp = runner1.val + carry;
            carry = tmp / 10;
            ListNode newnode = new ListNode(tmp%10);
            pre.next = newnode;
            pre = newnode;
            runner1 = runner1.next;
        }
        while(runner2 != null){
            int tmp = runner2.val + carry;
            carry = tmp / 10;
            ListNode newnode = new ListNode(tmp%10);
            pre.next = newnode;
            pre = newnode;
            runner2 = runner2.next;
        }
        if(carry == 1){
            ListNode newnode = new ListNode(carry);
            pre.next = newnode;
        }
        return fakehead.next;
            
    }
}