15. check power of four .

 

4⁰  = 1      = 0000001      = 1bit

4¹  = 4      = 0000100      = 3bit

4²  = 16    = 0010000      = 5bit

4³  = 64    = 1000000      = 7bit

Three observations :

1 . number of set bit for each number is always  = 1

2 . ( n & (n-1) )  == 0

3 . Total bits is always hold odd number of bits

Code :

#include<bits/stdc++.h> using namespace std; int main() {     int n,i;      cin>>n;      if((n&(n-1))==0)     {         int cnt = 0;         while(n>0)         {            cnt++;            n= n>>1;         }         if(cnt&1)         cout<<"power of 4\n";         else cout<<"no\n";     }     else cout<<"no\n";   }