【ZOJ 3609】Modular Inverse

#include<cstdio>
#define ll long long

ll exgcd(ll a,ll b,ll &x,ll &y)
{
    if(b==0)
    {
        x=1;
        y=0;
        return a;
    }
    ll r=exgcd(b,a%b,y,x);
    y-=a/b*x;
    return r;
}

int main()
{
    ll t,a,m,x,y;
    scanf("%lld",&t);
    while(t--)
    {
        scanf("%lld%lld",&a,&m);
        int ok=exgcd(a,m,x,y);
        if(ok==1)
        {
            x=(x%m+m)%m;
            if(x==0)x=m;
            printf("%lld\n",x);
        }
        else
        {
            printf("Not Exist\n");
        }
    }
    return 0;
}