轮子实现

import java.util.*;

public class Main {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);

        double n = sc.nextDouble();
        double l = -10000, r = 10000;
        while (r - l > 1e-8) {//注意要比题目精度大二即可
            double mid = (l + r) / 2;
            if (mid * mid * mid > n) r = mid;
            else l = mid;
        }

        System.out.printf("%.6f", r);
    }
}

库函数Math.cbrt(cube root)函数求解

import java.util.*;

public class Main {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);

        double n = sc.nextDouble();

        double ans = Math.cbrt(n);
        System.out.printf("%.6f", ans);
    }
}