快速幂&快速乘

LL mult_mod(LL a, LL b, LL c)

{

    a %= c; b %= c;

    LL ret = 0;

    LL tmp = a;

    while (b){

        if (b & 1){

            ret += tmp; 

            if (ret > c) ret -= c;//直接取模慢很多

        }

        tmp <<= 1;

        if (tmp > c) tmp -= c;

        b >>= 1;

    }

    return ret;

}



LL pow_mod(LL a, LL n, LL mod)

{

    LL ret = 1;

    LL temp = a%mod;

    while (n){

        if (n & 1) ret = mult_mod(ret, temp, mod);

        temp = mult_mod(temp, temp, mod);

        n >> 1;

    }

    return ret;

}