1class Solution {2    public ListNode mergeKLists(ListNode[] lists) {3        PriorityQueue<ListNode> heap = new PriorityQueue<>(Comparator.comparingInt(n -> n.val));4        for (ListNode head : lists) if (head != null) heap.offer(head);5        ListNode dummy = new ListNode(0), tail = dummy;6        while (!heap.isEmpty()) {7            ListNode current = heap.poll();8            tail.next = current;9            tail = current;10            if (current.next != null) heap.offer(current.next);11        }12        return dummy.next;13    }14}