模板 ：快速幂 && 快速乘

• 注意在乘的过程中不要爆long long ,如果爆了转为快速乘

快速幂

int power(int a, int b, int mod){
    int ans = 1 % mod;
    while(b){
        if(b&1) ans = (long long)ans * a % mod;
        a = (long long) a*a %mod;
        b >>= 1;
    }
    return ans;
}

快速乘

typedef unsigned long long ULL;
ULL mul() {
    ULL a, b, p;
    cin >> a >> b >> p;
    ULL res = 0;
    while (a) {
        if (a & 1) res = (res + b) % p;
        b = (b + b) % p;
        a >>= 1;
    }
    return res;
}