给你一个链表数组，每个链表都已经按升序排列。

请你将所有链表合并到一个升序链表中，返回合并后的链表。

/*** Definition for singly-linked list.* public class ListNode {*     int val;*     ListNode next;*     ListNode() {}*     ListNode(int val) { this.val = val; }*     ListNode(int val, ListNode next) { this.val = val; this.next = next; }* }*/
class Solution {/*public static void main(String[] args) {ListNode[] lists = new ListNode[3];lists[0] = new ListNode(1);lists[0].add(4);lists[0].add(5);lists[1] = new ListNode(1);lists[1].add(3);lists[1].add(4);lists[2] = new ListNode(2);lists[2].add(2);lists[2].add(6);ListNode res = mergeKLists(lists);}*/public static ListNode mergeKLists(ListNode[] lists) {ListNode headNode = new ListNode();ListNode curNode = headNode;int len = lists.length;if (len == 0) {return null;}if (!len1(lists)) {return null;}for (int i = 0; i < len; i = (i + 1) % len) {if (!len1(lists)) {return headNode.next;}int index = min1(lists);ListNode newNode = new ListNode();newNode.val = lists[index].val;lists[index] = lists[index].next;curNode.next = newNode;curNode = newNode;}return headNode.next;}private static int min1(ListNode[] lists) {int i = 0;while (lists[i] == null) {i++;}for (int j = i + 1; j < lists.length; j++) {while (j < lists.length && lists[j] == null) {j++;}if (j < lists.length && lists[j].val < lists[i].val) {i = j;}}return i;}private static boolean len1(ListNode[] lists) {for (int i = 0; i < lists.length; i++) {if (lists[i] != null) {return true;}}return false;}
}