• 要根据exponent是正数还是负数进行讨论，另外要考虑base=0 的情况，利用递归来实现O(logn)的时间
    class Solution:
  def Power(self, base, exponent):
      # write code here
      if base == 0:return 0
      if exponent >= 0: return  self.PowerWithUnsignedExponent(base, exponent)
      if exponent < 0: return  1.0/self.PowerWithUnsignedExponent(base, (-1)*exponent)
  def PowerWithUnsignedExponent(self, base, exponent):
      if exponent == 0:
          return 1
      if exponent == 1:
          return base
      res = self.PowerWithUnsignedExponent(base, exponent//2)
      res *= res
      if exponent % 2 == 1:
          res *= base
      return res
  • 优化代码，将Exponent右移一位相当于除以2，将Exponent与1做与运算，得1为奇数，得0为偶数
          res = self.PowerWithUnsignedExponent(base, exponent>>1)
      res *= res
      if exponent & 0x1 == 1:
          res *= base
      return res