326. Power of Three

Given an integer, write a function to determine if it is a power of three.web Follow up: Could you do it without using any loop / recursion?svg s思路: 1. 看是否3的指數，即判斷n==3^i。直接的方法就是每次和3求餘，若是爲０，就除以3,看是否等於１

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