---
title: 'LeetCode 342. Power of Four'
disqus: hackmd
---

# LeetCode 342. Power of Four

## Description

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

An integer n is a power of four, if there exists an integer x such that n == 4^x^.

## Example

Input: n = 16
Output: true

Input: n = 1
Output: true

## Constraints

-2^31^ <= x <= 2^31^ - 1

## Answer

4的次方必是2的次方，先將小於0和非2次方篩掉，4的次方數-1必整除3，故檢查餘數為0者為答案。

//2021_11_09
bool isPowerOfFour(int num) {
    if((num & (num - 1)) || num < 1){return false;}
    return ((num - 1) % 3) == 0;
}

## Link
https://leetcode.com/problems/power-of-four/
###### tags: `Leetcode`