1 /* Min heap*/
2 public class Solution {
3 public ListNode mergeKLists(ArrayList<ListNode> lists) {
4 if(lists.size()<=0) return null;
5
6 Comparator<ListNode> comparator = new Comparator<ListNode>(){
7 public int compare(ListNode m,ListNode n){
8 return m.val-n.val;
9 }
10 };
11 PriorityQueue<ListNode> pq = new PriorityQueue<ListNode>(lists.size(),comparator);
12 for(int i=0;i<lists.size();i++){
13 if(lists.get(i)!=null){
14 pq.add(lists.get(i));
15 }
16 }
17 ListNode safe = new ListNode(-1);
18 ListNode pre = safe;
19 while(!pq.isEmpty()){
20 pre.next = pq.poll();
21 pre = pre.next;
22 if(pre.next!=null)
23 pq.add(pre.next);
24 }
25 return safe.next;
26 }
27 }
