题解 | #求解立方根#

import java.util.Scanner;
import java.util.concurrent.atomic.DoubleAdder;

import java.math.BigDecimal;
import java.math.RoundingMode;
// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        double sysValue = in.nextDouble();
        BigDecimal sysDouble = new BigDecimal(sysValue).abs();
        double value = sysDouble.doubleValue();
        DoubleAdder atomicDouble = new DoubleAdder();
        test(value, atomicDouble, value);
        double resultValue = atomicDouble.doubleValue();

        BigDecimal resultBi = BigDecimal.valueOf(resultValue).setScale(1,
                              RoundingMode.HALF_EVEN);
        BigDecimal va = new BigDecimal("0.1");
        BigDecimal multiply;
        do {
            resultBi = resultBi.add(va);
            multiply = resultBi.multiply(resultBi).multiply(resultBi);
        } while (multiply.doubleValue() < value);

        BigDecimal subtractResult = resultBi.subtract(va);
        BigDecimal abs = multiply.subtract(sysDouble).abs();
        BigDecimal abs1 = subtractResult.multiply(subtractResult).multiply(
                              subtractResult).subtract(sysDouble).abs();
        if (abs.compareTo(abs1) < 0) {
            test2(sysValue, resultBi);
        } else {
            test2(sysValue, subtractResult);
        }
    }

    private static void test(Double sysChangeValue, DoubleAdder atomicDouble,
                             double sysValue) {
        if (sysChangeValue * sysChangeValue * sysChangeValue < sysValue) {
            atomicDouble.add(sysChangeValue);
            return;
        } else {
            sysChangeValue = sysChangeValue / 2;
            test(sysChangeValue, atomicDouble, sysValue);
        }
    }

    private static void test2(double sysValue, BigDecimal v) {
        if (sysValue > 0) {
            System.out.println(v);
        } else {
            System.out.println("-" + v);
        }
    }
}