int val;

ListNode *next;

ListNode() : val(0), next(nullptr) {}

ListNode(int x) : val(x), next(nullptr) {}

ListNode(int x, ListNode *next) : val(x), next(next) {}

ListNode* mergeKLists(std::vector<ListNode*>& lists);

static void test()

{

ListNode node3{5};

ListNode node2{4, &node3};

ListNode node1{1, &node2};

ListNode node6{4};

ListNode node5{3, &node6};

ListNode node4{1, &node5};

ListNode node8{6};

ListNode node7{2, &node8};

Solution23 s;

std::vector<ListNode *> lists{&node1, &node4, &node7};

auto res = s.mergeKLists(lists);

}