https://leetcode.com/problems/power-of-three/description/
题目
Given an integer, write a function to determine if it is a power of three.
Follow up: Could you do it without using any loop / recursion?
题目翻译
题目解析
判断一个数是不是3的幂。
参考答案
class Solution {
public:
bool isPowerOfThree(int n) {
if(n <= 0) return false;
//3 9 27 81
//big3 % n == 0
//big3 = 3^k
//k = log3(maxint);
const int maxint = 0x7fffffff;
int k = log(maxint)/log(3);
int big3 = pow(3, k);
return big3 % n == 0;
}
};
