checker 疑似没有判长度为 1 的区间

for (int l = 0; l < n; l++)
    for (int r = l + 1; r < n; r++) {
        int resp = grader::ask(std::vector<int>(p.begin() + l, p.begin() + r + 1));
        int resq = grader::ask(std::vector<int>(q.begin() + l, q.begin() + r + 1));
        if (resp != resq) {
            std::cout << "Wrong answer." << std::endl;
            return 0;
        }
    }