Merge k Sorted Lists

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

 1 public class Solution {
 2     public ListNode mergeKLists(ArrayList<ListNode> lists) {
 3         // Start typing your Java solution below
 4         // DO NOT write main() function
 5         if(lists.size()==0) return null;
 6         PriorityQueue<ListNode> q = new PriorityQueue<ListNode>(lists.size(),new Comparator<ListNode>(){
 7             public int compare(ListNode a, ListNode b){
 8                 return a.val>b.val?1:(a.val==b.val?0:-1);
 9                 }
10             });
11         
12         for(ListNode list:lists){
13             if(list!=null) q.add(list);
14         }
15                 
16         ListNode head = new ListNode(0), prev = head;
17         while(q.size()!=0){
18             ListNode temp = q.poll();
19             prev.next = temp;
20             if(temp.next!=null) q.add(temp.next);
21             prev = prev.next;
22         }
23         return head.next;
24     }
25 }

第二遍：

 1 public class Solution {
 2     public ListNode mergeKLists(ArrayList<ListNode> lists) {
 3         // Start typing your Java solution below
 4         // DO NOT write main() function
 5         if(lists.size()==0) return null;
 6         ListNode header = new ListNode(-1), cur = header;
 7         while(true){
 8             int pos = -1;
 9             for(int i = 0; i < lists.size(); i ++){
10                 if(lists.get(i) != null && (pos == -1 || lists.get(i).val < lists.get(pos).val))
11                     pos = i;
12             }
13             if(pos != -1){
14                 cur.next = lists.get(pos);
15                 cur = cur.next;
16                 lists.set(pos,lists.get(pos).next);
17             }else{
18                 break;
19             }
20         }
21         return header.next;
22     }
23 }