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

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode mergeKLists(List<ListNode> lists) {
        ListNode head=new ListNode(-1);
        ListNode tail=head;
        if(lists.size()<=0) return null;
        Comparator<ListNode> mycmp=new Comparator<ListNode>()
        {
            public int compare(ListNode l1,ListNode l2)
            {
                if(l1.val>l2.val) return 1;
                else if(l1.val<l2.val)return -1;
                return 0;
                
                
                
            }
            
        } ;
        
        PriorityQueue<ListNode> prq=new PriorityQueue<ListNode>(lists.size(),mycmp);
        for(ListNode n:lists)
        {
            if(n!=null)
            {
                prq.add(n);
            }
            
        }
        while(prq.size()>0)
        {
            ListNode tem=prq.poll();
            tail.next=tem;
            tail=tail.next;
            if(tem.next!=null)
            {
                prq.add(tem.next);
            }
    
            
        }
        
            return head.next;
        
        
        
        
        
    }
}