triangles

    private int triangles(int[][] a) {
        int plus = 0;
        for (int i = 0; i < 3; i++) {
            int diag = 1;
            for (int j = 0; j < 3; j++)
                diag *= a[j][(i + j) % 3];
            plus += diag;
        }

        int minus = 0;
        for (int i = 2; i >= 0; i--) {
            int diag = 1;
            for (int j = 0; j < 3; j++)
                diag *= a[j][(i - j + 3) % 3];
            minus += diag;
        }

        return plus - minus;
    }