LeetCode - 两数相加 - JavaScript解法

主要思路就是按位相加，判断是否大于10，然后判断链表末尾是否为0

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} l1
 * @param {ListNode} l2
 * @return {ListNode}
 */
var addTwoNumbers = function(l1, l2) {
    let head = new ListNode(0);
    let ret = head;
    while(l1 || l2){
        if(l1){
            if(l2){
                ret.val += l1.val + l2.val
                l2 = l2.next;
            }else{
              ret.val += l1.val
                l2 = l2
            }
            l1 = l1.next
        }else{
            if(l2){
              ret.val += l2.val
              l2 = l2.next
            }else{
                l2 = l2
            }
            l1 = l1
        }
        if(ret.val >= 10){
           ret.val = ret.val % 10;
           ret.next = new ListNode(1);
        }
        ret.next = ret.next || new ListNode(0);
        if(l1 == null && l2 == null){
            if(ret.next.val === 0){
                ret.next = null
            }
        }
        ret = ret.next
    }
    return head;
};