快速幂（带模板子）

long long fastPower(long long base, long long power,long long k) {
    long long result = 1;
    while (power > 0) {
        if (power & 1) //此处等价于if(power%2==1)
        {
            result = result * base % k;
        }
        power >>= 1;//此处等价于power=power/2,位右移操作 
        base %= k;//避免base * base 溢出
        base = (base * base) % k;
    }
    return result;
}