MergeKLists

public ListNode mergeKLists(ListNode[] lists) {

        if(lists==null||lists.length==0) return null;

        PriorityQueue<ListNode> minHeap=new PriorityQueue<>((o1, o1)->{

            return o1.val-o2.val;

        });

        for(int i=0; i<lists.length; i++){

            if(lists[i]!=null) minHeap.add(lists[i]);

        }

        ListNode head = new ListNode(0);

        ListNode p=head;

        while(minHeap.size()>0){

            ListNode temp=minHeap.poll();

            p.next=temp;

            p=p.next;

            if(temp.next!=null){

                minHeap.add(temp.next);

            }

        }

        return head.next;

    }