HDU 1395 2^x mod n = 1

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2^x mod n = 1

Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 15873 Accepted Submission(s): 4937

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

Author

MA, Xiao

Source

ZOJ Monthly, February 2003

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题意很简单，不多说了，直接看代码吧

#include<stdio.h>
#include<string.h>
int main()
{
	int n,m,i,j,k,l;
	while(scanf("%d",&n)!=EOF)
	{
		m=1;
		int ans=0;
		if(n%2==0||n==1)
		printf("2^? mod %d = 1\n",n);
		else
		{
			while(1)
			{
				m=m*2;
			    m=m%n;
			    ans++;
			    if(m==1)
			    {
			   	   break;
			    }
			}
			printf("2^%d mod %d = 1\n",ans,n);
			
		}
	}
	return 0;
}