ZOJ 3609 Modular Inverse

Modular Inverse

Time Limit: 2 Seconds Memory Limit: 65536 KB

The modular modular multiplicative inverse of an integer a modulo m is an integer x such that a-1≡x (mod m). This is equivalent to ax≡1 (mod m).

Input

There are multiple test cases. The first line of input is an integer T ≈ 2000 indicating the number of test cases.

Each test case contains two integers 0 < a ≤ 1000 and 0 < m ≤ 1000.

Output

For each test case, output the smallest positive x. If such x doesn’t exist, output “Not Exist”.

Sample Input

3

3 11

4 12

5 13

Sample Output

4

Not Exist

8

#include <iostream>
#include <string.h>
#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <algorithm>

using namespace std;
int a,m;
int tag[1005];
int ans;
int main()
{
int t;
scanf("%d",&t);
while(t--)
{
scanf("%d%d",&a,&m);
int x=1;
bool flag=true;
memset(tag,0,sizeof(tag));
while(1)
{
if(((a*x)%m)==(1%m))
{ans=x;break;}
else
{
x++;
int num=(a*x)%m;
if(tag[num])
{
flag=false;
break;
}
tag[num]=1;

}
}
if(!flag)
printf("Not Exist\n");
else
printf("%d\n",ans);
}
return 0;
}