leetcode刷題，總結，記錄，備忘 342

leetcode342

Power of Four

Given an integer (signed 32 bits), write a function to check whether it is a power of 4.

Example:

Given num = 16, return true. Given num = 5, return false.

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

Credits:

Special thanks to @yukuairoy for adding this problem and creating all test cases.

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使用高中數學的對數公式，如果不是4個指數次幂的話，結果一定是帶小數位的數，是以轉換成int類型然後再和這個結果比看是否相同就可以判斷是不是4的指數次幂了。

class Solution {
public:
    bool isPowerOfFour(int num) {
        if (num <= 0)
        {
            return false;
        }
        
        return log(num) / log(4) == (int)(log(num) / log(4));
    }
};