/*
Method 1:
	Algorithm: SHIFT and count the number of 1
	Integer的范围是(-2^31) ~ (2^31-1), 32位是符号位
*/
public boolean isPowerOfTwo(int a) {
	int count = 0;
	for(int i=0;i<31;i++) {
		if(((a>>i) & 1) == 1) {
			count++;
		}
	}
	return count <=1;
}

/*
Method 2:
3 =     11
4 =   100
7 =   111
8 = 1000
所有的power of 2 number都有一个特性 number & (number -1) =  0
*/
public boolean isPowerOfTwo(int a) {
	if(a < 1) {
		return false;
	}
	return (a & (a-1)) == 0;
}