public ListNode mergeKLists(ListNode[] lists) {

        if(lists == null || lists.length == 0)

           return null;

        if(lists.length == 1)

           return lists[0];

        return recursion(lists,0,lists.length - 1);

    }

    //recursion

    public ListNode recursion(ListNode[] lists,int start,int end){

        if(start == end)//只有一个链表

           return lists[start];

        if(start < end){

            int mid = start + (end - start) / 2; //注意：这里防止整数越界的处理,start+(end-start)/2

            ListNode l1 = recursion(lists,start,mid);

            ListNode l2 = recursion(lists,mid + 1,end);

            return merge(l1,l2);

        } else

            return null;

    }

    //merge

    public ListNode merge(ListNode l1,ListNode l2){

        ListNode head = new ListNode(0); //创建一个头结点，最后还要删掉

        ListNode p = head;

        while(l1 != null && l2 != null){

            if(l1.val <= l2.val){

                p.next = l1;

                l1 = l1.next;

            } else{

                p.next = l2;

                l2 = l2.next;

            }

            p = p.next;

        }

        p.next = (l1 != null) ? l1 : l2;

        return head.next;// head的下一个节点是第一个数据结点

    }