public class Solution {

public ListNode addTwoNumbers(ListNode l1, ListNode l2) {

ListNode ret = new ListNode(0);

ListNode curr = ret;

int carry = 0;

int v1, v2;

while (l1 != null || l2 != null) {

if (l1 == null) {

v1 = 0;

} else {

v1 = l1.val;

l1 = l1.next;

}

if (l2 == null) {

v2 = 0;

} else {

v2 = l2.val;

l2 = l2.next;

}

int s = v1 + v2 + carry;

carry = s / 10;

curr.next = new ListNode(s % 10);

curr = curr.next;

}

if (carry == 1) {

curr.next = new ListNode(1);

}

return ret.next;

}

public ListNode makeNumber(int n) {

ListNode ret = new ListNode(0);

ListNode curr = ret;

while (n > 0) {

ListNode e = new ListNode(n % 10);

curr.next = e;

curr = e;

n /= 10;

}

return ret.next;

}

public void printNumber(ListNode e) {

while (e != null) {

System.out.format("%d", e.val);

e = e.next;

}

System.out.format("\n");

}

public static void main(String[] args) {

Solution s = new Solution();

ListNode n1 = s.makeNumber(1);

ListNode n2 = s.makeNumber(999);

s.printNumber(n1);

s.printNumber(n2);

ListNode res = s.addTwoNumbers(n1, n2);

s.printNumber(res);

}

}

class ListNode {

int val;

ListNode next;

ListNode(int x) {

val = x;

next = null;

}

}