text: /**
   * Diagonal difference is the absolute difference of the sums of all elements in both diagonals.
   * Example:
   * a b c
   * d e f
   * g h i
   * diff = abs((a + e + i) - (c + e + g))
   */
  long long diagonal_diff(const vector<vector<int>>& arr) {
      const auto size = arr.size();
      auto diff{0};
      for (auto i = 0; i < size; i++) {
          diff += arr[i][i];
          diff -= arr[i][size - i - 1];
      }
      return abs(diff);
  }
  