add-two-numbers.js

/**
 * 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 result = new ListNode();
    let n = result;
    let carry = 0;
    let noMoreL1 = false, noMoreL2 = false;

    do
    {                    
        let v1 = 0, v2 = 0;

        if (l1) v1 = l1.val;
        if (l2) v2 = l2.val;

        let sum = v1 + v2 + carry;

        if (sum >= 10)
        {
            n.val = sum % 10;
            carry = 1;
        }
        else
        {            
            n.val = sum;            
            carry = 0;
        }

        if (l1 && !l1.next) noMoreL1 = true;
        if (l2 && !l2.next) noMoreL2 = true;
        
        if ((l1 && l1.next) || (l2 && l2.next) || carry == 1)
        {
            n.next = new ListNode();            
            n = n.next;
            if (noMoreL1 && noMoreL2) n.val = 1;
        }        

        if (noMoreL1 && noMoreL2) break;

        if (l1 && l1.next) l1 = l1.next; else l1 = null;
        if (l2 && l2.next) l2 = l2.next; else l2 = null;

    } while (true);

    return result;

};