【C語言】 LeetCode 326 Power of Three

題目

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?

方法一：

由于整形存儲有大小限制，利用其大小限制可以快速求解。（一般用32位，4個位元組）

bool isPowerOfThree(int n) {
    int const Max3PowerInt = 1162261467; // 3^19, 3^20 = 3486784401 > MaxInt32
    if (n <= 0 || n > Max3PowerInt) return false;
    return Max3PowerInt % n == 0;
}
           

方法二：

利用數學方法進行轉換計算，但是算法複雜度還是較高

bool isPowerOfThree(int n) {
    int const Max3PowerInt = 1162261467; // 3^19, 3^20 = 3486784401 > MaxInt32
    if (n <= 0 || n > Max3PowerInt) return false;
    return Max3PowerInt % n == 0;
}