Method matrix

code/data-structures/matrix.cpp:7–8

  int rows, cols, cnt; vector<T> data;
  inline T& at(int i, int j) { return data[i * cols + j]; }
  matrix(int r, int c) : rows(r), cols(c), cnt(r * c) {
    data.assign(cnt, T(0)); }
  matrix(const matrix& other) : rows(other.rows),
    cols(other.cols), cnt(other.cnt), data(other.data) { }
  T& operator()(int i, int j) { return at(i, j); }