leetcode刷题，总结，记录，备忘 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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使用高中数学的对数公式，如果不是4个指数次幂的话，结果一定是带小数位的数，所以转换成int类型然后再和这个结果比看是否相同就可以判断是不是4的指数次幂了。

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