求逆元（線性求逆元）及其擴展歐幾里得

線性求逆元模板：

int inv[maxn];
void initInverse(){
    inv[1] = 1;
    for(int i = 2; i <= maxn; i++)
        inv[i] = (p - p/i) * inv[p % i] % p;
}

 

擴展歐幾里得模板

LL exgcd(LL a, LL b, LL &x, LL &y){
    if(b == 0){
        x = 1; y = 0;
        return a;
    }
    LL ans = exgcd(b, a % b, x, y);

    LL tmp = x; x = y; y = tmp - a/b * y;
    return ans;
}