[leetcode] 326. Power of Three

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?

check n =? 3^x

Solution 1

Idea: divide 3 to see whether get 0 residue

class Solution {
public:
bool isPowerOfThree(int n) {
while (n!=0 && n%3==0){
n= n/3;
}
return n==1;
}
};

Solution 2

Idea: if n=3^x, then log10(n) = xlog10(3), log10(n)/log10(3) is integer

class Solution {
public:
bool isPowerOfThree(int n) {
if (n < 0)
return false;
else{
return (int(log10(n)/log10(3))-(log10(n)/log10(3)) ==0);
}

}
};