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
");
        else
            printf("%d
",ans);
    }
    return 0;
}