# Recursive Java solution(easy to understand)

• ``````/**
* public class ListNode {
*     int val;
*     ListNode next;
*     ListNode(int x) { val = x; }
* }
*/
public class Solution {
public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
}

private ListNode addTwoNumbers(ListNode l1, ListNode l2, int carryOnFromLow) {
// node == null means all digits from list the node belongs to are added to sum
if (l1 == null && l2 == null) {
if (carryOnFromLow == 1) {
return new ListNode(1);
} else {
return null;
}
}
int operand1 = l1 == null ? 0 : l1.val;
int operand2 = l2 == null ? 0 : l2.val;
int sum = (operand1 + operand2 + carryOnFromLow) % 10;
int carryOnToHigh = (operand1 + operand2 + carryOnFromLow) / 10;
ListNode sumNode = new ListNode(sum);
// keep calculating until l1 == null && l2 == null
sumNode.next = addTwoNumbers(l1 == null ? null: l1.next, l2 == null ? null : l2.next, carryOnToHigh);
return sumNode;
}
}
``````

Looks like your connection to LeetCode Discuss was lost, please wait while we try to reconnect.