题解 | #求解立方根#

#include <iostream>
#include <iomanip>
using namespace std;

//求解立方根
class SolveCubeRoot {
  private:
    double n;

  public:
    //构造函数
    SolveCubeRoot(const double a);

    //析构函数
    ~SolveCubeRoot();

    //立方
    const double cube(const double i)const;

    //立方根
    const double cubeRoot(const double lower = -3, const double upper = 3)const;
};

SolveCubeRoot::SolveCubeRoot(const double a) {
    this->n = a;
    return;
}

SolveCubeRoot::~SolveCubeRoot() {
}

const double SolveCubeRoot::cube(const double i) const {
    return i * i * i;
}

const double SolveCubeRoot::cubeRoot(const double lower,
                                     const double upper) const {
    //由于输入值的绝对值不超过20，可以将最初的边界选为[-3,3]
    double mid = (lower + upper) / 2;
    double cube1 = this->cube(lower);
    double cube2 = this->cube(mid);
    double cube3 = this->cube(upper);
    if (cube2 == this->n)
        return mid;
    if (cube3 - cube1 < 0.1)
        return mid;
    if (cube2 > this->n)
        return this->cubeRoot(lower, mid);
    else
        return this->cubeRoot(mid, upper);
}

int main() {
    double a;
    while (cin >> a) { // 注意 while 处理多个 case
        cout << fixed << setprecision(1) << SolveCubeRoot(a).cubeRoot() << endl;
    }
}
// 64 位输出请用 printf("%lld")