p231

 
public class  {
    public boolean isPowerOfTwo(int n) {
        if (n == 2 || n == 1)
			return true;
		int[] a = new int[35];
		a[0] = 2;
		for (int i = 1; i < 32; i++) {
			a[i] = 2 * a[i - 1];
			if (n < a[i])
				break;	//最好跳出
			if (n == a[i])
				return true;
			//System.out.println(n+"   "+a[i]);
		}
		return false;
    }
}