c++如何将数组插入哈希集

C++ how to insert array into hash set?

本文关键字：插入 哈希集 数组 c++      更新时间：2023-10-16

我需要在哈希集中插入一个1D数组。

但是在编译时出现了错误。

#include <stdio.h>
#include <stdlib.h>
#include <hash_set.h>
using namespace std;
int hash_comp(const int* state1,const int* state2) {
    int result = 0;
    for (i = 0; i < 16; i++) 
    {
        if (state1[i] != state2[i]) {
            result = -1;
        }
    }
    return result;
}
struct eqArray
{
    bool operator()(const int* a1,const int* a2) const
  {
    return hash_comp(a1,a2) == 0;
  }
};
hash_set<int*,hash<int*>,eqArray> closelist;
int main(int argc, char** argv)
{
   const int sn[16] = {1,2,3,4,5,6,0,8,9,10,11,12,13,14,7,15};
   closelist.insert(sn);
   return 0;
}

/usr/include/c++/4.2.1/ext/hashtable.h: In member function 'size_t __gnu_cxx::hashtable<_Val, _Key, _HashFcn, _ExtractKey, _EqualKey, _Alloc>::_M_bkt_num_key(const _Key&, size_t) const [with _Val = int*, _Key = int*, _HashFcn = __gnu_cxx::hash<int*>, _ExtractKey = std::_Identity<int*>, _EqualKey = std::equal_to<int*>, _Alloc = std::allocator<int*>]':
/usr/include/c++/4.2.1/ext/hashtable.h:599:   instantiated from 'size_t __gnu_cxx::hashtable<_Val, _Key, _HashFcn, _ExtractKey, _EqualKey, _Alloc>::_M_bkt_num(const _Val&, size_t) const [with _Val = int*, _Key = int*, _HashFcn = __gnu_cxx::hash<int*>, _ExtractKey = std::_Identity<int*>, _EqualKey = std::equal_to<int*>, _Alloc = std::allocator<int*>]'
/usr/include/c++/4.2.1/ext/hashtable.h:1006:   instantiated from 'void __gnu_cxx::hashtable<_Val, _Key, _HashFcn, _ExtractKey, _EqualKey, _Alloc>::resize(size_t) [with _Val = int*, _Key = int*, _HashFcn = __gnu_cxx::hash<int*>, _ExtractKey = std::_Identity<int*>, _EqualKey = std::equal_to<int*>, _Alloc = std::allocator<int*>]'
/usr/include/c++/4.2.1/ext/hashtable.h:437:   instantiated from 'std::pair<__gnu_cxx::_Hashtable_iterator<_Val, _Key, _HashFcn, _ExtractKey, _EqualKey, _Alloc>, bool> __gnu_cxx::hashtable<_Val, _Key, _HashFcn, _ExtractKey, _EqualKey, _Alloc>::insert_unique(const _Val&) [with _Val = int*, _Key = int*, _HashFcn = __gnu_cxx::hash<int*>, _ExtractKey = std::_Identity<int*>, _EqualKey = std::equal_to<int*>, _Alloc = std::allocator<int*>]'
/usr/include/c++/4.2.1/ext/hash_set:197:   instantiated from 'std::pair<typename __gnu_cxx::hashtable<_Value, _Value, _HashFcn, std::_Identity<_Tp>, _EqualKey, _Alloc>::const_iterator, bool> __gnu_cxx::hash_set<_Value, _HashFcn, _EqualKey, _Alloc>::insert(const typename __gnu_cxx::hashtable<_Value, _Value, _HashFcn, std::_Identity<_Tp>, _EqualKey, _Alloc>::value_type&) [with _Value = int*, _HashFcn = __gnu_cxx::hash<int*>, _EqualKey = std::equal_to<int*>, _Alloc = std::allocator<int*>]'
src/ods2.cpp:677:   instantiated from here

如果你使用std::array<int, 16>而不是int*，你所有的问题都会消失。如果你没有c++ 11编译器，你可以使用boost::array代替。同时，将hash_set替换为unordered_set。

似乎没有std::hash对std::array s的专门化，所以我自己写了:

#include <unordered_set>
#include <array>
namespace std
{
    template<typename T, size_t N>
    struct hash<array<T, N> >
    {
        typedef array<T, N> argument_type;
        typedef size_t result_type;
        result_type operator()(const argument_type& a) const
        {
            hash<T> hasher;
            result_type h = 0;
            for (result_type i = 0; i < N; ++i)
            {
                h = h * 31 + hasher(a[i]);
            }
            return h;
        }
    };
}
std::unordered_set<std::array<int, 16> > closelist;
int main()
{
    std::array<int, 16> sn = {1,2,3,4,5,6,0,8,9,10,11,12,13,14,7,15};
    closelist.insert(sn);
}

您没有发布实际的错误消息，只发布了跟踪。也就是说，这可能是因为你的数据集使用非const int*，而你的数据是const。

也就是说，我建议使用unordered_set而不是hash_set(无论是从std::tr1，如果你的编译器支持，或从std，如果你的编译器支持c++ 11或从Boost)，并听取弗雷德的建议，使用{std,boost}::array而不是原始指针。

我认为不存在专门的hash<int*>。我添加了这个:

namespace __gnu_cxx{ //I'm not sure what compiler version you used,
                     //mine wanted this
    template<>
    struct hash<const int*>{
        size_t operator()(const int*a) const{
            size_t r = 0;
            for (int i=0;i<16;i++)
                r = (r<<1) ^ a[i]; //not sure if it makes sense as a hash.
            return r;
        }
    };
}

我还放了一些const s，它编译了

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