Description

Implement pow(x, n), which calculates x raised to the power n (xn).

Example 1:

Input: 2.00000, 10
Output: 1024.00000

Example 2:

Input: 2.10000, 3
Output: 9.26100

Example 3:

Input: 2.00000, -2
Output: 0.25000
Explanation: 2-2 = 1/22 = 1/4 = 0.25

Note:

  • -100.0 < x < 100.0
  • n is a 32-bit signed integer, within the range [−231, 231 − 1]

Solutions

　　注意 n 为负数的情况！

# Time: O(logn)
# Space: O(1)
class Solution:
    def myPow(self, x: float, n: int) -> float:
        if n == 0:
            return 1
        if n < 0:
            n = -n
            x = 1 / x
        res = 1
        while n != 0:
            if n % 2 == 1:
                res *= x
            x *= x
            n >>= 1
        return res
# 304/304 cases passed (28 ms)
# Your runtime beats 65.82 % of python3 submissions
# Your memory usage beats 100 % of python3 submissions (12.8 MB)

References

  1. 50. Pow(x, n)