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

 1 /**

 2  * Definition for singly-linked list.

 3  * public class ListNode {

 4  *     int val;

 5  *     ListNode next;

 6  *     ListNode(int x) {

 7  *         val = x;

 8  *         next = null;

 9  *     }

10  * }

11  */

12 public class Solution {

13     public ListNode mergeKLists(List<ListNode> lists) {

14         ListNode head=new ListNode(-1);

15         ListNode tail=head;

16         if(lists.size()<=0) return null;

17         Comparator<ListNode> mycmp=new Comparator<ListNode>()

18         {

19             public int compare(ListNode l1,ListNode l2)

20             {

21                 if(l1.val>l2.val) return 1;

22                 else if(l1.val<l2.val)return -1;

23                 return 0;

24                 

25                 

26                 

27             }

28             

29         } ;

30         

31         PriorityQueue<ListNode> prq=new PriorityQueue<ListNode>(lists.size(),mycmp);

32         for(ListNode n:lists)

33         {

34             if(n!=null)

35             {

36                 prq.add(n);

37             }

38             

39         }

40         while(prq.size()>0)

41         {

42             ListNode tem=prq.poll();

43             tail.next=tem;

44             tail=tail.next;

45             if(tem.next!=null)

46             {

47                 prq.add(tem.next);

48             }

49     

50             

51         }

52         

53             return head.next;

54         

55         

56         

57         

58         

59     }

60 }

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