Merge k Sorted Lists

1public ListNode mergeKLists(ListNode[] lists) {
2    PriorityQueue<ListNode> heap = new PriorityQueue<>((a, b) -> a.val - b.val);
3
4    // Add the head of each list to the min-heap
5    for (ListNode list : lists) {
6        if (list != null) {
7            heap.offer(list);
8        }
9    }
10
11    ListNode dummy = new ListNode(0);
12    ListNode current = dummy;
13
14    // Continuously extract the minimum element
15    while (!heap.isEmpty()) {
16        ListNode node = heap.poll();
17        current.next = node;
18        current = current.next;
19
20        if (node.next != null) {
21            heap.offer(node.next);
22        }
23    }
24
25    return dummy.next;
26}