flipMatrix2.cpp

using Coord = std::pair<int, int>;
using Matrix = std::vector<vector<int>>;

int read_int()
{
    int i;
    std::cin >> i;
    return i;
}

std::vector<int> read_line(int n)
{
    std::vector<int> line;
    std::generate_n(std::back_inserter(line), 2 * n, read_int);
    return line;
}

Matrix read_matrix()
{
    Matrix m;
    int n = read_int();
    std::generate_n(std::back_inserter(m), 2 * n, [=]{ return read_line(n); });
    return m;
}

std::vector<int> symetric_values(Matrix const& m, int n, Coord const& c)
{
    int i = c.first;
    int j = c.second;
    int max = 2 * n - 1;
    return { m[i][j]
           , m[max-i][j]
           , m[i][max-j]
           , m[max-i][max-j] };
}

int best_quadrant(Matrix const& m)
{   
    int n = m.size() / 2;
    int sum = 0;
    for (int i = 0; i < n; ++i)
    {
        for (int j = 0; j < n; ++j)
        {
            auto flips = symetric_values(m, n, {i, j});
            sum += *std::max_element(flips.begin(), flips.end());
        }
    }
    return sum;
}

int main()
{
    int n = read_int();
    std::generate_n(std::ostream_iterator<int>(std::cout, "\n"), n, []{
        return best_quadrant(read_matrix());
    });
    return 0;
}