Merge k Sorted Lists

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

Solution:

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode mergeKLists(ListNode[] lists) {
        ListNode dummy = new ListNode(0);
        ListNode scan = dummy;
        
        if(lists.length==0) return dummy.next;
        
        PriorityQueue<ListNode> pq = new PriorityQueue<>(lists.length, (a,b)->(a.val-b.val));
        for(ListNode ln : lists) if(ln!=null) pq.offer(ln);
        
        while(!pq.isEmpty()){
            scan.next = pq.poll();
            scan = scan.next;
            if(scan.next!=null) pq.offer(scan.next);
        }
        return dummy.next;
    }
}