Code-Storm2019/50_Power.py at master · AutuanLiu/Code-Storm2019 · GitHub

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# https://blog.csdn.net/MosBest/article/details/69264953
# 二进制法
# Runtime: 40 ms, faster than 71.63% of Python3 online submissions for Pow(x, n).
# Memory Usage: 13.2 MB, less than 5.53% of Python3 online submissions for Pow(x, n).
# 快速幂算法
class Solution:
    def myPow(self, x: float, n: int) -> float:
        if not -100.0 < x < 100.0:
            return
        return self.pow1(x, n) if n >= 0 else 1.0 / self.pow1(x, -n)

    def pow1(self, x, n):
        ans = 1.0
        while n != 0:
            if n % 2 == 1:
                ans *= x
            x *= x
            n //= 2
        return ans


# Runtime: 44 ms, faster than 38.51% of Python3 online submissions for Pow(x, n).
# Memory Usage: 13.2 MB, less than 5.53% of Python3 online submissions for Pow(x, n).
# 二分幂法
# 时间复杂度 O(log_2^n)
# 空间复杂度 O(1)
class Solution:
    def myPow(self, x: float, n: int) -> float:
        if not -100.0 < x < 100.0:
            return
        return self.pow1(x, n) if n >= 0 else 1.0 / self.pow1(x, -n)

    def pow1(self, x, n):
        if n == 0:
            return 1
        if n == 1:
            return x
        ans = self.pow1(x, n // 2)
        ans *= ans
        if n % 2 == 1:
            ans *= x
        return ans


# 递归法 求x^n
class Solution:
    def myPow(self, x: float, n: int) -> float:
        if not -100.0 < x < 100.0:
            return
        return self.pow1(x, n) if n >= 0 else 1.0 / self.pow1(x, -n)

    def pow1(self, x, n: int):
        ans = 1.0
        if n == 0:
            return 1
        else:
            return x * self.pow1(x, n - 1)


# 循环法 求x^n
class Solution:
    def myPow(self, x: float, n: int) -> float:
        if not -100.0 < x < 100.0:
            return
        return self.pow1(x, n) if n >= 0 else 1.0 / self.pow1(x, -n)

    def pow1(self, x, n: int):
        ans = 1.0
        while n != 0:
            ans *= x
            n -= 1
        return ans


# Runtime: 40 ms, faster than 71.63% of Python3 online submissions for Pow(x, n).
# Memory Usage: 13.2 MB, less than 5.53% of Python3 online submissions for Pow(x, n).
# 使用系统自带方法
class Solution:
    def myPow(self, x: float, n: int) -> float:
        return x**n


# Runtime: 40 ms, faster than 71.63% of Python3 online submissions for Pow(x, n).
# Memory Usage: 13.4 MB, less than 5.53% of Python3 online submissions for Pow(x, n).
# 使用系统自带方法
class Solution:
    def myPow(self, x: float, n: int) -> float:
        return pow(x, n)