Leetcode Merge k Sorted Lists

 1 package Merge.k.Sorted.Lists;
 2 
 3 import java.util.ArrayList;
 4 import java.util.Comparator;
 5 import java.util.List;
 6 import java.util.PriorityQueue;
 7 import java.util.function.Function;
 8 import java.util.function.ToDoubleFunction;
 9 import java.util.function.ToIntFunction;
10 import java.util.function.ToLongFunction;
11 
12 public class MergekSortedLists1 {
13     public ListNode mergeKLists(List<ListNode> lists) {
14         if(lists==null||lists.size()==0) return null;
15         int size=lists.size();
16         PriorityQueue <ListNode>queue=new PriorityQueue<ListNode>(size,new Comparator<ListNode>(){
17             public int compare(ListNode o1, ListNode o2) {
18                 return o1.val-o2.val;
19             }    
20         });
21         for(ListNode head:lists){
22             if(head!=null)
23             queue.offer(head);
24         }
25         ListNode head=null;
26         ListNode index=null;
27         while(!queue.isEmpty()){
28             ListNode min=queue.poll();
29             if(head==null){
30                 head=min;
31                 index=min;
32                 
33             }else{
34                 index.next=min;
35                 index=index.next;
36             }
37             ListNode curr=min;
38             curr=curr.next;
39             if(curr!=null)
40             queue.offer(curr);
41         }
42         return head;        
43     }
44     public static void main(String args[]){
45         MergekSortedLists1 service=new MergekSortedLists1();
46         List<ListNode> lists=new ArrayList<ListNode>();
47         ListNode n1=new ListNode(1);
48         ListNode n2=new ListNode(2);
49         ListNode n3=new ListNode(2);
50         n1.next=n2;
51         n2.next=n3;
52         ListNode x1=new ListNode(1);
53         ListNode x2=new ListNode(1);
54         ListNode x3=new ListNode(2);
55         x1.next=x2;
56         x2.next=x3;
57         lists.add(n1);
58         lists.add(x1);
59         ListNode head=service.mergeKLists(lists);
60         while(head!=null){
61             System.out.println(head.val);
62             head=head.next;
63         }
64     }
65     
66 }