typedef long long ll;//擴充套件gcd求解x,y同時還把gcd(a,b)求出來了，exgcd的返回值就是gcd(a,b)
ll exgcd(ll a, ll b, ll &x, ll &y)    
{  
    if(b == 0)  
    {  
        x = 1;  
        y = 0;  
        return a;  
    }  
    ll d = exgcd(b, a % b, x, y);  
    ll t = x;  
    x = y;  
    y = t - (a / b) * y;  
    return d;  
} 
 

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