51node1256 乘法匿元（扩展欧几里得）

#include<iostream>
using namespace std;

int gcd(int a,int b,int &x,int &y){
    if (b==0){
        x=1,y=0;
        return a;
    }
    int q=gcd(b,a%b,y,x);
    y-=a/b*x;
    return q;
}

int main()
{
    int n, m, x, y;
    cin>>m>>n;
    gcd(m, n, x, y);
    cout<<(x+n)%n<<endl;
    return 0;
}

　　为保持手感