dart-exercism/difference-of-squares/lib/difference_of_squares.dart

class DifferenceOfSquares {
  int squareOfSum(int num) {
    int sum = num * (num + 1) ~/ 2;
    return sum * sum;
  }

  int sumOfSquares(int num) {
    return num * (num + 1) * (2 * num + 1) ~/ 6;
  }

  int differenceOfSquares(int num) {
    return squareOfSum(num) - sumOfSquares(num);
  }
}

void main(List<String> args) {
  final differenceOfSquares = DifferenceOfSquares();
  print(differenceOfSquares.differenceOfSquares(100).abs());
}