扩展欧几里得求线性同余方程

https://www.acwing.com/problem/content/880/

#include <bits/stdc++.h>
using namespace std;

int ex_gcd(int a,int b,int &x,int &y)
{
    if (!b)
    {
        x=1,y=0;
        return a;
    }
    int d=ex_gcd(b,a%b,y,x);
    y-=a/b*x;
    return d;
}
int main()
{
    int t;
    scanf("%d",&t);
    while(t--)
    {
        int a,b,m;

        int x,y;
        cin>>a>>b>>m;
        int d=ex_gcd(a,m,x,y);
        if(b%d) 
            puts("impossible");
        else 
            printf("%lld\n",(long long)b/d*x%m);
    }
    return 0;
}