Find whether a given number is a power of 4 or not | GeeksforGeeks

3. A number n is a power of 4 if following conditions are met.
a) There is only one bit set in the binary representation of n (or n is a power of 2)
b) The count of zero bits before the (only) set bit is even.

bool isPowerOfFour(unsigned int n)

{

  int count = 0;

  /*Check if there is only one bit set in n*/

  if ( n && !(n&(n-1)) )

  {

     /* count 0 bits before set bit */

     while(n > 1)

     {

       n  >>= 1;

       count += 1;

     }     

 

    /*If count is even then return true else false*/

    return (count%2 == 0)? 1 :0;

  }

  /* If there are more than 1 bit set

    then n is not a power of 4*/

  return 0;

}

Another solution is to keep dividing the number by 4, i.e, do n = n/4 iteratively. In any iteration, if n%4 becomes non-zero and n is not 1 then n is not a power of 4, otherwise n is a power of 4.

bool isPowerOfFour(int n)

{

  if(n == 0)

    return 0;

  while(n != 1)

  {   

   if(n%4 != 0)

      return 0;

    n = n/4;     

  }

  return 1;

}

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