LeetCode23 合并多个排序链表

Merge k sorted linked lists and return it as one sorted list. Analyze and describe its complexity.

Example:

Input:
[
1->4->5,
1->3->4,
2->6
]
Output: 1->1->2->3->4->4->5->6

public ListNode mergeKLists(ListNode[] lists) {
        if(lists == null || lists.length == 0) return null;
        PriorityQueue<ListNode> queue = new PriorityQueue<ListNode>(new Comparator<ListNode>(){
           public int compare(ListNode a, ListNode b){
               return a.val - b.val;
           } 
        });
        for(ListNode node : lists){
            if(node != null){
                queue.add(node);
            }
        }
        ListNode dummy = new ListNode(0);
        ListNode tail = dummy;
        while(!queue.isEmpty()){
            tail.next = queue.poll();
            tail = tail.next;
            if(tail.next != null){
                queue.add(tail.next);
            }
        }
        return dummy.next;
    }