Merge k Sorted Lists

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

题目大意：合并k个排序好的链表，分析复杂度

题目难度：Hard

import java.util.*;

/**
 * Created by gzdaijie on 16/5/9
 * 优先队列,相当于最小堆,每次取出最小值,如果有后续节点,入队
 * 复杂度O(N*K*log(K)) => N个数，维护K大小的优先队列（因为每次出队，至多入队一个）
 */
public class Solution {
    public ListNode mergeKLists(ListNode[] lists) {
        if (lists == null || lists.length == 0) return null;

        Queue<ListNode> queue = new PriorityQueue<ListNode>(10, new Comparator<ListNode>() {
            @Override
            public int compare(ListNode o1, ListNode o2) {
                if (o1.val > o2.val) return 1;
                if (o1.val < o2.val) return -1;
                return 0;
            }
        });

        for (int i = 0; i < lists.length; i++) {
            if (lists[i] != null) queue.add(lists[i]);
        }

        ListNode head = new ListNode(0);
        ListNode p = head;
        while (!queue.isEmpty()) {
            p.next = queue.poll();
            p = p.next;
            if (p.next != null) {
                queue.add(p.next);
            }
            p.next = null;
        }
        return head.next;
    }
}