231. Power of Two

Look at binary of an integer. If an integer is a power of two, it must contains only one "1" in its binary. Also, all the negative integers and zero are not power of two.

1:  class Solution {  
2:  public:  
3:    bool isPowerOfTwo(int n) {  
4:      if (n <= 0) return false;  
5:      while (!(n & 1)) {  
6:        n >>= 1;  
7:      }  
8:      return !(n >> 1) ? true : false;  
9:    }  
10:  };  

The following solution is inspired by counting number of ones in a integer.

1:  class Solution {  
2:  public:  
3:    bool isPowerOfTwo(int n) {  
4:      return n > 0 && (n & (n - 1)) == 0;  
5:    }  
6:  };