SOURCE

/**
 * 输入：l1 = [2,4,3], l2 = [5,6,4]
 * 输出：[7,0,8]
 * 解释：342 + 465 = 807
 * @param {ListNode} l1
 * @param {ListNode} l2
 * @return {ListNode}
 */
var addTwoNumbers = function (l1, l2) {

    var l1_h = l1.reverse();
    var l2_h = l2.reverse();
    l1_h.length > l2_h.length ? '' : [l1_h, l2_h] = [l2_h, l1_h];;
    var outArr = [];
    var one = 0;
    var he = 0
    l1_h.forEach((item, i) => {
        var c2 = l2_h[i] > 0 ? l2_h[i] : 0
        one > 0 ? he = item + c2 + 1 : he = item + c2;
        he < 10 ? one = 0 : one = 1;
        he >= 10 ? he = he - 10 : '';
        outArr.push(he)
    })
    one > 0 ? outArr.push(1) : one = 0;
    return outArr
};

addTwoNumbers([2, 4, 3], [5, 6, 4]);
addTwoNumbers([9, 9, 9, 9, 9, 9, 9], [9, 9, 9, 9]);

console.log(addTwoNumbers([2, 4, 3], [5, 6, 4]), addTwoNumbers([9, 9, 9, 9, 9, 9, 9], [9, 9, 9, 9]))