Merge k sorted linked lists into one sorted linked list?

ListNode MergeKLists(ListNode[] lists) {

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

PriorityQueue<ListNode, int> pq = new PriorityQueue<ListNode,

int>();

foreach (var list in lists)

if (list != null)

pq.Enqueue(list, list.val);

ListNode dummy = new ListNode(0);

ListNode current = dummy;

while (pq.Count > 0) {

var node = pq.Dequeue();

current.next = node;

current = current.next;

if (node.next != null)

pq.Enqueue(node.next, node.next.val);

return dummy.next;

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Explanation:

Use a min-heap (priority queue) to always pick the smallest head node among k lists.