50.pow-x-n.py

#
# @lc app=leetcode.cn id=50 lang=python3
#
# [50] Pow(x, n)
#

# @lc code=start
class Solution:
    def myPow(self, x: float, n: int) -> float:
        # recursion version
        # if not n:
        #     return 1
        # if n < 0:
        #     return 1 / self.myPow(x, -n)
        # if n % 2 != 0:
        #     return x * self.myPow(x, n-1)
        # return self.myPow(x * x, n/2)

        if n < 0:
            x = 1 / x
            n = -n
        res = 1
        while n:
            if n & 1:
                res *= x
            x *= x
            n >>= 1
        return res
# @lc code=end