text: /*
  21. Merge Two Sorted Lists
  Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.
  */
  
  /**
   * Definition for singly-linked list.
   * function ListNode(val) {
   *     this.val = val;
   *     this.next = null;
   * }
   */
  /**
   * @param {ListNode} l1
   * @param {ListNode} l2
   * @return {ListNode}
   */
  var mergeTwoLists = function (l1, l2) {
    'use strict'
    const dummy = {next: null}
    let pre = dummy
    while (l1 && l2) {
      if (l1.val < l2.val) {
        pre.next = l1
        l1 = l1.next
      } else {
        pre.next = l2
        l2 = l2.next
      }
      pre = pre.next
    }
  
    if (l1 === null) pre.next = l2
    else pre.next = l1
    return dummy.next
  }
  
  module.exports = mergeTwoLists
  