/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} l1
 * @param {ListNode} l2
 * @return {ListNode}
 */
var addTwoNumbers = function(l1, l2) {
    let newHead = new ListNode(0);
    let tempPointer = newHead;
    let carry = 0
    
    while (l1 || l2 || carry !== 0) {
        if (l1) {
            carry += l1.val;
            l1 = l1.next;
        }
        
        if (l2) {
            carry += l2.val;
            l2 = l2.next;
        }
        
        tempPointer.next = new ListNode(carry % 10);
        tempPointer = tempPointer.next;
        carry = Math.floor(carry / 10);
    }
    return newHead.next;
};