[Sword refers to the offer problem solution: java] the integer power of the value

topic

Given a floating-point base of type double and an integer exponent of type int. Find the exponent power of base.

Ensure that base and exponent are not 0 at the same time

answer

1. Use built-in functions

/**
     * 使用内置函数
     *
     * @param base
     * @param exponent
     * @return
     */
    public double Power(double base, int exponent) {
    
    
        return Math.pow(base, exponent);
    }

2. Violence Law

Violent law: direct multiplication

Note :

If the power is negative, we rewrite it as the exponent square of the original number

Processing code :

if (exponent < 0) {
    
    //如果为负数，需要进行处理
     base = 1 / base;
     exponent = -1 * exponent;
}

Complete code

  /**
     * 暴力法：直接相乘
     *
     * @param base
     * @param exponent
     * @return
     */
    public double Power2(double base, int exponent) {
    
    
        //1、判断次方的正负
        if (exponent == 0) return 1.0;
        if (exponent < 0) {
    
    //如果为负数，需要进行处理
            base = 1 / base;
            exponent = -1 * exponent;
        }
        double sum = 1.0;
        //直接循环即可
        for (int i = 0; i < exponent; i++) {
    
    
            sum *= base;
        }
        return sum;
    }

3. Recursion method (power exponent)

 /**
     * 递归法：快速幂
     *
     * @param base
     * @param exponent
     * @return
     */
    public double Power3(double base, int exponent) {
    
    
        if (exponent == 0) return 1.0;
        if (exponent < 0) {
    
    //先对次方做处理
            exponent = -1 * exponent;
            base = 1 / base;
        }
        return q_power(base,exponent);
    }

    public double q_power(double b, int e) {
    
    
        if (e == 0) return 1.0;
        double ret = Power3(b, e / 2);
        if (e % 2 == 0) {
    
    //偶数
            return ret * ret;
        } else {
    
    //奇数
            return ret * ret * b;
        }
    }