23. Merge k Sorted Lists

public class Solution {
    private static final Comparator<ListNode> listComparator = new Comparator<ListNode>() {
        @Override
        public int compare(ListNode x, ListNode y) {
            return x.val - y.val;
        }
    };
    public ListNode mergeKLists(ListNode[] lists) {
        if (lists.length == 0) return null;
        Queue<ListNode> q = new PriorityQueue<ListNode>(lists.length, listComparator);

        for (ListNode node : lists) {
            if (node != null) {
                q.add(node);
            }
        }

        ListNode dummy = new ListNode(0);
        ListNode prev = dummy;
        while (!q.isEmpty()) {
            ListNode minNode = q.poll();
            prev.next = minNode;
            prev = prev.next;

            if (minNode.next != null) {
                q.add(minNode.next);
            }
        }

        return dummy.next;
    }
}