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
1. Binary Search
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)