杭电1395 2^x mod n = 1

2^x mod n = 1

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 11642    Accepted Submission(s): 3625

Problem Description

Give a number n, find the minimum x(x>0) that satisfies 2^x mod n = 1.

 

Input

One positive integer on each line, the value of n.

 

Output

If the minimum x exists, print a line with 2^x mod n = 1.

Print 2^? mod n = 1 otherwise.

You should replace x and n with specific numbers.

 

Sample Input

2 5

 

Sample Output

2^? mod 2 = 1 2^4 mod 5 = 1

//参考讨论区代码
#include
int main()
{
	int n;
	while(scanf("%d",&n)!=EOF)
	{
		if(n%2==0||n==1)
		printf("2^? mod %d = 1\n",n);	
		else
		{
			int k=1;
			__int64 i=2;
			while(1)
			{
				if(i%n==1)
				{
				printf("2^%d mod %d = 1\n",k,n);
				break;
				}
				i=(i%n)<<1;//不太理解为什么不对n取余会超时
				k++;	
			}
		}
	}
return 0;
}