@SAMM: Something like this might work:
bool PowerOfThree(unsigned int n)
{
int powsof2[5] = {16,8,4,2,1};
int powsof3[32] =
{1,3,0,9,27,0,81,243,0,729,0,2187,6561,0,19683,59049,0,177147,0,531441,1594323,0,
4782969,14348907,0,43046721,129140163,0,387420489,0,1162261467,3486784401};
int i,j=0;
unsigned int m = n;
for( i = 0 ; i < 5 ; ++i )
{
if( m >> powsof2[i] )
{
j += powsof2[i];
m >>= powsof2[i];
}
}
return powsof3[j] == n;
}
The for loop determines the bit number of the highest-order bit set.
The table of powers of three is indexed by the bit number of the
highest bit set.
Dave
On Nov 28, 2:47 am, SAMMM <[email protected]> wrote:
> Given a number u have to check whether the number(N) can be expressed
> in the form 3^n = N i:e It can be expressed in terms of power of 3.
>
> It can be done taking log on both but I am looking an alternate
> approach (bit manipulation) .
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