数值的整数次方

image.png

最基础的解法，就是循环地乘以base，这里有一个问题，当指数为0和负数时候的处理。

# -*- coding:utf-8 -*-
class Solution:
    def Power(self, base, exponent):
        # write code here
        ans = 1
        if exponent > 0:
            for i in range(exponent):
                ans *= base
        elif exponent == 0:
            return 1
        else:
            for i in range(-1*exponent):
                ans *= base
            ans = 1 / ans
        return ans

书中给出的优化的算法：

image.png

# -*- coding:utf-8 -*-
class Solution:
    def Power(self, base, exponent):
        # write code here
        if exponent == 0:
            return 1
        if exponent == 1:
            return base
        flag = False
        if exponent < 0:
            flag = True
            exponent *= -1
        result = self.Power(base, exponent >> 1)
        result *= result
        if exponent & 0x1 == 1:
            result *= base
        if flag == True:
            return 1/result
        return result