合并K个有序链表

输入:
[
  1->4->5,
  1->3->4,
  2->6
]
输出: 1->1->2->3->4->4->5->6

    public ListNode mergeKLists(ListNode[] lists) {
   if (lists==null||lists.length==0){
            return null;
        }
        //造个小根堆,以链表头结点得值排序得小根堆
        PriorityQueue<ListNode> MinHeap=new PriorityQueue<>(new Comparator<ListNode>() {
            @Override
            public int compare(ListNode o1, ListNode o2) {
                return o1.val-o2.val;
            }
        });

        for (ListNode head: lists ){
            if (head==null){
                continue;
            }
            MinHeap.add(head);
        }
        ListNode head=new ListNode(1);
        ListNode curr=head;
        while (!MinHeap.isEmpty())
        {
            ListNode out=MinHeap.poll();
            curr.next=out;
            curr=curr.next;
            if (out.next!=null){
                MinHeap.add(out.next);
            }
        }
        return head.next;
    }