326. Is the square root of 3 ispowerofthree

Own version

  
 

   
  

  
public static bool IsPowerOfThree(int n) {
   
  

  
if (n == 1) {
   
  

  
return true;
   
  

  
}
   
  

  
double num = n;
   
  

  
bool isPower = false;
   
  

  
while (num >= 1) {
   
  

  
num = num / 3;
   
  

  
if (num == 1 && num == (int)num) {
   
  

  
return true;
   
  

  
}
   
  

  
}
   
  

  
return isPower;
   
  

  
}
  
 

Recursive version

  
 

   
  

  
public static bool IsPowerOfThree(int n) {
   
  

  
if (n == 1) {
   
  

  
return true;
   
  

  
} else if (n == 0 || n % 3 > 0) {
   
  

  
return false;
   
  

  
} else {
   
  

  
return IsPowerOfThree(n / 3);
   
  

  
}
   
  

  
}
  
 

Finally, there is a clever way to make use of the logarithm of the change of the formula to do, the high school has learned the bottom formula for log AB = LogCB/logCA, then if N is a multiple of 3, then log3n must be an integer, we can write it as log by using the change formula3n = Log10N/log103, note here must use 10 as the base, can not use the natural number or 2 as the base, otherwise when the n=243 error, the reason please seeThis post. Now the question becomes a judgment log.10N/log103 is an integer, in C + + to determine whether the number A is an integer, we can use A-int (a) = = zero to determine, see the code is as follows:

           
          

            
           

           
class Solution {
            
           

           
public:
            
           

           
 bool isPowerOfThree(int n) {
            
           
 return (N> 0 && int(log10(N) /log10(3)) -log10(N) /log10(3) == 0);
            
           

           
 }
            
           

           
};
           
          

From for notes (Wiz)

326. Is the square root of 3 ispowerofthree