79 lines
1.8 KiB
C++
79 lines
1.8 KiB
C++
//
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// Created by light on 19-11-4.
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//
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#include <iostream>
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#include <unordered_set>
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#include <complex>
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using namespace std;
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class Customer {
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};
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// 形式一 通过一个类，重载了操作符()的方式，形成了一个仿函数（函数对象）
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class CustomerHash {
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public:
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size_t operator()(const Customer &c) const {
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// return ...;
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}
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};
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// 形式二 这个方法实际是通过指定了一个函数指针的方式来通知容器，对于这个自定义类到底应该使用哪个hash function
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size_t customer_hash_func(const Customer &t) {
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// return ...;
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}
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// 形式三 以struct hash 偏特化形式实现hash function
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namespace std { // 必须放在std里面
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template<>
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struct hash<Customer> : public __hash_base<size_t, Customer> { // 继承不继承都可以!
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size_t
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operator()(const Customer&s) const noexcept {
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// return ...;
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}
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};
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}
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// 万能的HashFunction 使用variadic templates
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// (4)
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template<typename T>
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inline void hash_combine(size_t& seed, const T& val){
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seed = std::hash<T>()(val) + 0x9e3779b9
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+ (seed << 6) + (seed >> 2);
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}
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// (3)
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template<typename T>
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inline void hash_val(size_t& seed, const T& val){
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hash_combine(seed, val);
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}
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// (2)
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template<typename T, typename... Types>
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inline void hash_val(size_t& seed, const T& val, const Types&... args){
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hash_combine(seed, val);
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hash_val(seed, args...);
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}
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// (1)
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template<typename... Types>
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inline size_t hash_val(const Types&... args){
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size_t seed = 0;
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hash_val(seed, args...);
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return seed;
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}
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int main() {
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unordered_set<Customer, CustomerHash> unorderedSet;
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unordered_set<Customer,size_t(*)(const Customer&)>custset(20,customer_hash_func);
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unordered_set<Customer> unset;
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int *p= reinterpret_cast<int *>(new Customer());
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cout<<hash_val(p)<<endl;
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return 0;
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}
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