ListNode* create_tree(int s) {
    if (s == 0)
        return nullptr;
    ListNode* root = new ListNode(1);
    create_node(root, 1, s);
    return root;
}
void create_node(ListNode* head, int index, int s) {
    if (index * 2 <= s) {
            ListNode* left = new ListNode(index * 2, nullptr, nullptr, head);
            head->left = left;
            create_node(left, index * 2, s);
        }
    if (index * 2 + 1 <= s) {
        ListNode* right = new ListNode(index * 2 + 1, nullptr, nullptr, head);
        head->right = right;
        create_node(right, index * 2 + 1, s);
    }

}