/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode[]} lists
 * @return {ListNode}
 */
var mergeKLists = function(lists) {
    if (!lists || lists.length <= 0) return null
    if (lists.length === 1) return lists[0]
    let currentList = lists[0]
    for (let i = 1; i < lists.length; i++) {
        currentList = mergeKList(currentList, lists[i])
    }
    return currentList
};
/**
* 合并两个链表
* @param {ListNode[]} 链表
* @return {ListNode}
*/
var mergeKList = function (l1, l2) {
    if (!l1) return l2
    if (!l2) return l1
    let newList = new ListNode(null)
    if (l1.val < l2.val) {
        newList.val = l1.val
        newList.next = mergeKList(l1.next, l2)
    } else {
        newList.val = l2.val
        newList.next = mergeKList(l1, l2.next)
    }
    return newList
}