docs: private int countAboveThreshold(int[][] mat, double threshold) {
      int ret = 0;
      for(int i = 0; i < mat.length; i++) {
        int[] row = mat[i];
        for(int j = 0; j < row.length; j++) {
          if(row[j] >= threshold) {
            ret++;
          }
        }
      }
      return ret;
    }