Hợp nhất danh sách được sắp xếp K

def merge_k_lists_opt(lists):
    if not lists: return []
    if isinstance(lists[0], list):
        nodes_list = [build_linked_list(l) for l in lists if l]
        res = merge_k_lists_opt_helper(nodes_list)
        return linked_list_to_list(res)
    return merge_k_lists_opt_helper(lists)

def merge_k_lists_opt_helper(lists) -> ListNode:
    import heapq
    heap = []
    for i, head in enumerate(lists):
        if head:
            heapq.heappush(heap, (head.val, i, head))
    dummy = ListNode(0)
    curr = dummy
    while heap:
        val, i, node = heapq.heappop(heap)
        curr.next = node
        curr = curr.next
        if node.next:
            heapq.heappush(heap, (node.next.val, i, node.next))
    return dummy.next

def merge_k_lists_brute(lists):
    if not lists: return []
    if isinstance(lists[0], list):
        nodes_list = [build_linked_list(l) for l in lists if l]
        res = merge_k_lists_brute_helper(nodes_list)
        return linked_list_to_list(res)
    return merge_k_lists_brute_helper(lists)

def merge_k_lists_brute_helper(lists) -> ListNode:
    vals = []
    for l in lists:
        curr = l
        while curr:
            vals.append(curr.val)
            curr = curr.next
    vals.sort()
    dummy = ListNode(0)
    curr = dummy
    for v in vals:
        curr.next = ListNode(v)
        curr = curr.next
    return dummy.next