一般矩阵乘法

struct Matrix {
    vector<vector<int>> M;
    Matrix(int n, int m) {
        M.assign(n, vector<int>(m, 0));
    }
    void read() {
        int n = M.size(), m = M[0].size();
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                cin >> M[i][j];
            }
        }
    }
    Matrix T() {
        int n = M.size(), m = M[0].size();
        Matrix t(m, n);
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                t.M[j][i] = M[i][j];
            }
        }
        return t;
    }
    void print() {
        int n = M.size(), m = M[0].size();
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                cout << M[i][j] << " \n"[j == m - 1];
            }
        }
    }
};

Matrix operator * (const Matrix &a, const Matrix &b) {
    int n = a.M.size(), m = a.M[0].size(), d = b.M[0].size();
    assert(m == b.M.size());
    Matrix c(n, d);
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < d; j++) {
            for (int k = 0; k < m; k++) {
                c.M[i][j] += a.M[i][k] * b.M[k][j];
            }
        }
    }
    return c;
}