2-6-dart_funcs.dart

import 'dart:math';

void main() {
  // 1.
  String text = 'hello world';
  revert(text);

  // 2.
  var ar = [1, 22, 3, 40, 12];
  var result = avg(ar);
  print(result);

  // 3.
  revert2();

  result = avg2();
  print(result);

  // 4.
  var solution = quadraticEqation(1, -8, 12);
  print(solution);
  solution = quadraticEqation(5, 3, 7);
  print(solution);
  solution = quadraticEqation(1, 6, 9);
  print(solution);
}

// 1.
void revert(text) {
  print(text.split(' ').reversed.join(' '));
}

// 2.
double avg(List<int> numbers) {
  if (numbers.isEmpty) {
    return 0;
  }

  var sum = numbers.reduce((acc, number) => acc += number);
  return sum / numbers.length;
}

// 3.
void revert2([String text = '']) {
  revert(text);
}

double avg2([List<int> numbers = const []]) {
  return avg(numbers);
}

// 4.
// Для простоты не стал обрабатывать неполные квадратные уравнения
String quadraticEqation(int a, int b, int c) {
  int calcDiscriminant(int a, int b, int c) {
    return (pow(b, 2) as int) - 4 * a * c;
  }

  int calcX1(int a, int b, int discriminant) {
    return (-b + sqrt(discriminant).toInt()) ~/ (2 * a);
  }

  int calcX2(int a, int b, int discriminant) {
    return (-b - sqrt(discriminant).toInt()) ~/ (2 * a);
  }

  int discriminant = calcDiscriminant(a, b, c);

  switch (discriminant.compareTo(0)) {
    case -1:
      return 'Корней нет.';
    case 0:
      var x1 = calcX1(a, b, discriminant);
      return 'Корень $x1.';
    default:
      var x1 = calcX1(a, b, discriminant);
      var x2 = calcX2(a, b, discriminant);
      return 'Корни $x1 и $x2.';
  }
}