445. Add Two Numbers II

#### QUESTION:

You are given two non-empty linked lists representing two non-negative integers. The most significant digit comes first and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Follow up: What if you cannot modify the input lists? In other words, reversing the lists is not allowed.

Example:

``````Input: (7 -> 2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 8 -> 0 -> 7
``````

#### SOLUTION:

``````public class Solution {
public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
Stack<ListNode> sa = new Stack<>();
Stack<ListNode> sb = new Stack<>();
while (l1!=null){
l1 = l1.next;
}
while (l2!=null){
l2 = l2.next;
}
int carry = 0;
ListNode head = new ListNode(0);
while (sa.size()!=0 || sb.size()!=0 || carry!=0){
int a=0,b=0;
if(sa.size()!=0) a = sa.pop().val;
if(sb.size()!=0) b = sb.pop().val;
int value = (a+b+carry)%10;
carry = (a+b+carry)/10;
ListNode tmp = new ListNode(value);