326.power-of-three

Statement

简体中文English

Metadata

• Link: 3 的幂
• Difficulty: Easy
• Tag: 递归 数学

给定一个整数，写一个函数来判断它是否是 3 的幂次方。如果是，返回 true ；否则，返回 false 。

整数 n 是 3 的幂次方需满足：存在整数 x 使得 n == 3x

 

示例 1：

输入：n = 27
输出：true

示例 2：

输入：n = 0
输出：false

示例 3：

输入：n = 9
输出：true

示例 4：

输入：n = 45
输出：false

 

提示：

• -231 <= n <= 231 - 1

 

进阶：你能不使用循环或者递归来完成本题吗？

Metadata

• Link: Power of Three
• Difficulty: Easy
• Tag: Recursion Math

Given an integer n, return true if it is a power of three. Otherwise, return false.

An integer n is a power of three, if there exists an integer x such that n == 3x.

 

Example 1:

Input: n = 27
Output: true

Example 2:

Input: n = 0
Output: false

Example 3:

Input: n = 9
Output: true

 

Constraints:

• -231 <= n <= 231 - 1

 

Follow up: Could you solve it without loops/recursion?

Solution

Python 3

from bisect import bisect_left


class Solution:
    def isPowerOfThree(self, n: int) -> bool:
        if n <= 0:
            return False

        x = bisect_left(range(20), n, key=lambda x: 3 ** x)
        return 3 ** x == n

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最后更新: October 11, 2023