445. Add Two Numbers II.java

class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        Stack<Integer> s1=new Stack<>();
        while(l1!=null){
            s1.push(l1.val);
            l1=l1.next;
        }
        Stack<Integer> s2=new Stack<>();
        while(l2!=null){
            s2.push(l2.val);
            l2=l2.next;
        }
        int carry=0;
        ListNode newHead=null;
        while(!s1.isEmpty()|| !s2.isEmpty()||carry!=0){
            int n1=s1.isEmpty()?0:s1.pop();
            int n2=s2.isEmpty()?0:s2.pop();
            int tmp=n1+n2+carry;
            ListNode newNode=new ListNode(tmp%10);
            newNode.next=newHead;
            newHead=newNode;
            carry=tmp/10;
        }
        return newHead;    
    }
}