random/custom_hash.hpp

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• Last update: 2022-05-01 12:00:28+09:00
• Include: #include "random/custom_hash.hpp"
• Link: http://xorshift.di.unimi.it/splitmix64.c
• Link: https://codeforces.com/blog/entry/62393

Code

#pragma once
#include <chrono>
#include <cstdlib>

struct custom_hash {
    // https://codeforces.com/blog/entry/62393
    static uint64_t splitmix64(uint64_t x) {
        // http://xorshift.di.unimi.it/splitmix64.c
        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 =
            std::chrono::steady_clock::now().time_since_epoch().count();
        return splitmix64(x + FIXED_RANDOM);
    }
};

// Usage
#include <unordered_map>
std::unordered_map<int, int, custom_hash> robust_unordered_map;

#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
gp_hash_table<int, null_type, custom_hash> robust_hash_table; // fast unordered_set / unordered_map

#line 2 "random/custom_hash.hpp"
#include <chrono>
#include <cstdlib>

struct custom_hash {
    // https://codeforces.com/blog/entry/62393
    static uint64_t splitmix64(uint64_t x) {
        // http://xorshift.di.unimi.it/splitmix64.c
        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 =
            std::chrono::steady_clock::now().time_since_epoch().count();
        return splitmix64(x + FIXED_RANDOM);
    }
};

// Usage
#include <unordered_map>
std::unordered_map<int, int, custom_hash> robust_unordered_map;

#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
gp_hash_table<int, null_type, custom_hash> robust_hash_table; // fast unordered_set / unordered_map

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