unordered_map防止大量哈希冲突

https://codeforces.com/blog/entry/62393?tdsourcetag=s_pcqq_aiomsg
貌似听说会有卡unordered_map的，有巨佬给出了解决方案。基于一个随机时间的种子再配上一些奇怪的数字让你的程序抖动得更强。

struct custom_hash {
    static uint64_t splitmix64(uint64_t x) {
        x += 0x9e3779b97f4a7c15;
        x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
        x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
        return x ^ (x >> 31);
    }

    size_t operator()(uint64_t x) const {
        static const uint64_t FIXED_RANDOM = chrono::steady_clock::now().time_since_epoch().count();
        return splitmix64(x + FIXED_RANDOM);
    }
};