check a int number is power of 2?

个人信息：就读于燕大本科软件工程专业 目前大三;

本人博客：google搜索“cqs_2012”即可;

个人爱好：酷爱数据结构和算法，希望将来从事算法工作为人民作出自己的贡献;

博客内容：how many does the factorial of n have zero?

博客时间：2014-5-7;

编程语言：Java ;

编程坏境：Windows 7 专业版 x64;

编程工具：jdk，eclipse x64;

制图工具：office 2010 ppt;

硬件信息：7G-3 笔记本;

my words

every problem has a or more solutions.

check a int number is power of 2?

eg: 1 = 2^0;

2 = 2^1;

4 = 2^2;

5 != 2^2 and 5 != 2^3

make true the function: bool  _check_power_2(int n)

program run out follows

0 false
1 true
2 true
3 false
4 true
5 false
6 false
7 false
8 true
9 false
10 false
11 false
12 false
13 false
14 false
15 false
16 true
17 false
18 false
19 false
20 false
21 false
22 false
23 false
24 false
25 false
26 false
27 false
28 false
29 false
30 false
31 false
32 true
33 false
34 false
35 false
36 false
37 false
38 false
39 false
40 false
41 false
42 false
43 false
44 false
45 false
46 false
47 false
48 false
49 false
50 false
51 false
52 false
53 false
54 false
55 false
56 false
57 false
58 false
59 false
60 false
61 false
62 false
63 false
64 true
65 false
66 false
67 false
68 false
69 false
70 false
71 false
72 false
73 false
74 false
75 false
76 false
77 false
78 false
79 false
80 false
81 false
82 false
83 false
84 false
85 false
86 false
87 false
88 false
89 false
90 false
91 false
92 false
93 false
94 false
95 false
96 false
97 false
98 false
99 false

as for a int number n

the binary data of n only have one 1, then it is, or not.

eg:

find regularity, the number of power of 2 only has one 1.

so if( n & (n-1) == 0 ) return true; else return false;

package test;


public class test {

	public static void main(String[] args) {
		for(int i=0;i<100;i++)
		{
			System.out.println(i+" "+_2_pow(i));
		}

	}
	static boolean _2_pow(int n)
	{
		if( n > 0 )
		{
			int i = (n-1) & n ;
			if(i == 0)
				return true;
			else return false;
		}
		else return false ;
	}


}