LeetCode 2. 两数相加

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/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} l1
 * @param {ListNode} l2
 * @return {ListNode}
 */

function ListNode(val) {
  this.val = val;
  this.next = null;
}

var addTwoNumbers = function (l1, l2) {
  const result = new ListNode(0);
  let cur = result;
  let flag = 0;

  while (l1 !== null || l2 !== null || flag) {
    let sum = flag;
    if (l1 !== null) {
      sum += l1.val;
      l1 = l1.next;
    }
    if (l2 !== null) {
      sum += l2.val;
      l2 = l2.next;
    }

    flag = Math.floor(sum / 10);
    sum = sum % 10;
    cur.next = new ListNode(sum);
    cur = cur.next;
  }
  return result.next;
};