数值的整数次方（Java实现）

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本文介绍了一种计算数值的整数次方的算法，包括常规解法和使用二分思想的优化解法。通过两个不同的方法实现，分别适用于不同场景的需求。文章提供了详细的代码实现，展示了如何处理边界情况，如底数为零且指数为负时的异常输入。


public class E16Power {
    //数值的整数次方
    //功能测试、边界测试、错误处理

    //常规解法
    public static double power_solution1(double base, int exponent){
        //底为零且指数为负时分母为零
        if (base == 0.0 && exponent < 0)
            throw new IllegalArgumentException("Illegal Input!");
        if (exponent == 0)
            return 1.0;
        //先计算exponent为正的情况
        double result = nonnegativePower1(base, Math.abs(exponent));
        if (exponent < 0)
            return 1.0 / result;
        else
            return result;
    }

    private static double nonnegativePower1(double base, int exponent){
        //exponent > 0
        double result = 1.0;
        int step = 0;
        while(step <= exponent){
            result *= base;
            step++;
        }
        return result;
    }

    //二分思想
    public static double power_solution2(double base, int exponent){
        if (base == 0.0 && exponent < 0)
            throw new IllegalArgumentException("Illegal Input!");
        double result = nonnegativePower2(base, Math.abs(exponent));
        if (exponent < 0)
            return 1.0 / result;
        else
            return result;
    }

    private static double nonnegativePower2(double base, int exponent){
        //exponent > 0
        //递归终止条件
        if (exponent == 0)
            return 1.0;
        if(exponent == 1)
            return base;

        double result = power_solution2(base, exponent >> 1);
        result *= result;
        //余数为1时
        if ((exponent & 0x1) == 1)
            result *= base;
        return result;
    }

    public static void main(String[] args){
        System.out.println(E16Power.power_solution2(2.5, 3));
        System.out.println(E16Power.power_solution2(2.5, -3));
        System.out.println(E16Power.power_solution2(2.5, 0));
        System.out.println(E16Power.power_solution2(0, 1));
        System.out.println(E16Power.power_solution2(0, 0));
        //System.out.println(E16Power.power_solution2(0, -1)); //IllegalArgumentException
    }
}