逆元模板

ll (ll a,ll b,ll c) 
{
    ll ans = 1;
    while(b)
    {
        if(b&1)   //相当于b%2==1
            ans = (ans*a)%c;
        a = (a*a)%c;
        b>>=1;    //相当于b/=2
    }
    return ans;
}
 
ll inv(ll b,ll c)   //计算b的逆元
{
    return quick_mod(b,c-2,c);
}
 
ll div(ll a,ll b,ll c)  //计算(a/b)%c
{
    return ((a%c)*(inv(b,c)%c))%c;
}

void ex_gcd(ll a, ll b, ll &d, ll &x, ll &y){
    if (!b) {d = a, x = 1, y = 0;}
    else{
        ex_gcd(b, a % b, d, y, x);
        y -= x * (a / b);
    }
}
 
ll inv(ll a, ll p){//如果不存在，返回-1  a,p互质
    ll d, x, y;
    ex_gcd(a, p, d, x, y);
    return d == 1 ? (x % p + p) % p : -1;
}

 
ll inv(ll t, ll p) {
    //求t关于p的逆元，注意:t要小于p，最好传参前先把t%p一下 ,即inv(a%p, p)求a对p的逆元
    return t == 1 ? 1 : (p - p / t) * inv(p % t, p) % p;
}

ll inv[maxn];
void Prepare_inv(ll n,ll M){
    inv[1]=1;
    for(ll i=2;i<=n;i++){
        inv[i]=(ll)(M-M/i)*inv[M%i]%M;
    }
}