剑指offer__04__数值的整数次方

题目

给定一个double类型的浮点数base和int类型的整数exponent。求base的exponent次方。不考虑大数问题

需要注意的地方

1. 基数为 0 ，指数为负的情况
2. 优化计算的次数，利用指数相乘的性质
3. 判断奇偶性使用位运算，节约计算量

代码

public class Solution {
    public double Power(double base, int exponent) {
        if ( exponent == 0)
            return 1.0;
        if (base == 0)
            return 0.0;
        boolean flag = true;
        double result = 1.0;
        if (exponent < 0) {
            exponent = 0 - exponent;
            flag = false;
            result = powerWithUnsignedExponenrt(base, exponent);
        } else {
             result = powerWithUnsignedExponenrt(base, exponent);
        }
        return flag == true ? result : 1/result;
    }
    public double powerWithUnsignedExponenrt(double base, int exponent) {
        if (exponent == 0)
            return 1.0;
        if (exponent == 1)
            return base;
        double result = powerWithUnsignedExponenrt(base, exponent >> 1);
        result *= result;
        if ((exponent & 0x1) == 1) {
            result *= base;
        }
        return result;
    }
}