Leetcode解题: Power of Three (326)

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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?

解法1：Loop

C++

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class Solution {
public:
    bool isPowerOfThree(int n) {
        if (n < 1) return false;
        while ( n >= 3) {
            if (n % 3 != 0) {
                return false;
            }
            n  = n / 3;
        }
        if (n == 1) {
            return true;
        }
        return false;
    }
};

Java

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解法2：Follow up

如果一个数是3^x，那么以3为底数做log，结果一定是整数。运用log3(x) = log10(x) / log10(3)
C++

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class Solution {
public:
    bool isPowerOfThree(int n) {
      double res = log10(n) / log10(3);
      return (res - (int)res) == 0;
    }
};