递归算法计算平方根和立方根

Question

当我运行我的代码工作有时但其他我得到这个错误:

Exception in thread "main" java.lang.StackOverflowError       
at squareroot.SquareRoot.GetSquareRoot (SquareRoot.java: 9)   
at squareroot.SquareRoot.GetSquareRoot (SquareRoot.java: 13)   
at squareroot.SquareRoot.GetSquareRoot (SquareRoot.java: 13)`

我正在检查我的代码并且我没有进入无限循环,请问我该如何解决这个问题？谢谢.

public static double GetSquareRoot(double n, double low, double high) {
    double sqrt = (low + high) / 2;
    if (sqrt*sqrt > n)
        return GetSquareRoot(n, low, sqrt);
    if (sqrt*sqrt < n)
        return GetSquareRoot(n, sqrt, high);
    return sqrt;
}
public static double Sqrt(double n){
    return GetSquareRoot(n, 0, n);
}

public static double GetCubicRoot(double n, double low, double high) {
    double cbrt = (low + high) / 2;
    if (cbrt*cbrt*cbrt > n)
        return GetCubicRoot(n, low, cbrt);
    if (cbrt*cbrt*cbrt < n)
        return GetCubicRoot(n, cbrt, high);
    return cbrt;
}
public static double Cbrt(double n) {
    return GetCubicRoot(n, 0, n);
}

public static void main(String[] args) {
    Scanner Input = new Scanner(System.in);

    double n = Input.nextDouble();
    double sqrt = Sqrt(n);
    double cbrt = Cbrt(n);

    System.out.println("Raiz cuadrada igual a: "+ sqrt);        
    System.out.println("Raiz cubica igual a: "+ cbrt);  

}

Answer 1

您的结果不可能达到最终条件,因为乘以数字不太可能产生确切的数字,您必须引入误差幅度,因为平方根通常不精确,浮点算法使用近似值,因为浮点限制.

public static double GetSquareRoot(double n, double low, double high) {
    double errorMargin = 0.001;        
    double sqrt = (low + high) / 2;
    double diff = sqrt*sqrt - n;
    if ( diff > errorMargin)
        return GetSquareRoot(n, low, sqrt);
    if ( -diff > errorMargin)
        return GetSquareRoot(n, sqrt, high);
    return sqrt;
}

Answer 2

您正在停止条件是"if n == num"而n和num是double.已知Double或Float数字不精确,因此可能永远不会满足此条件.而是使用它

if(Math.abs(sqrt*sqrt - n) < .001)
     return sqrt;

当两个数字之间的差异变得"足够小"时,这将停止.

Answer 3

当您使用double时,您应该使用delta double值.因为您的计算值可能与预期的不相等.

bool CompareDoubles2 (double A, double B) 
{
   diff = A - B;
   return (diff < EPSILON) && (-diff > EPSILON);
}