unordered_map无法在工作的C++中初始化？

Question

问题：给定一个字符串数组，将字母表组合在一起。你可以按任何顺序返回答案。

字形是一个单词或短语，通过重新排列一个不同的单词或短语的字母，通常使用所有的原始字母一次。

Example 1:

Input: strs = ["eat","tea","tan","ate","nat","bat"]
Output: [["bat"],["nat","tan"],["ate","eat","tea"]]

代码：

class Solution
{
public:
    vector<vector<string>> groupAnagrams(vector<string> &strs)
    {
        unordered_map <unordered_multiset <char>, vector<string>> mp1;
        for (c : strs)
        {
            unordered_multiset<char> ms1;
            for (char h : c)
                m1.insert(h);
            mp1[ms1].push_back(c);
        }
        vector<vector<string>> res;
        for (auto c : mp1)
            res.push_back(c.second);
        return res;
    }
};

错误：

Line 6: Char 67: error: call to implicitly-deleted default constructor of 'unordered_map<unordered_multiset<char>, vector<std::string>>' (aka 'unordered_map<unordered_multiset<char>, vector<basic_string<char>>>')
        unordered_map <unordered_multiset <char>, vector<string>> mp1;
                                                                  ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/unordered_map.h:141:7: note: explicitly defaulted function was implicitly deleted here
      unordered_map() = default;
      ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/unordered_map.h:105:18: note: default constructor of 'unordered_map<std::unordered_multiset<char, std::hash<char>, std::equal_to<char>, std::allocator<char>>, std::vector<std::__cxx11::basic_string<char>, std::allocator<std::__cxx11::basic_string<char>>>, std::hash<std::unordered_multiset<char, std::hash<char>, std::equal_to<char>, std::allocator<char>>>, std::equal_to<std::unordered_multiset<char, std::hash<char>, std::equal_to<char>, std::allocator<char>>>, std::allocator<std::pair<const std::unordered_multiset<char, std::hash<char>, std::equal_to<char>, std::allocator<char>>, std::vector<std::__cxx11::basic_string<char>, std::allocator<std::__cxx11::basic_string<char>>>>>>' is implicitly deleted because field '_M_h' has a deleted default constructor
      _Hashtable _M_h;
                 ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/hashtable.h:414:7: note: explicitly defaulted function was implicitly deleted here
      _Hashtable() = default;
      ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/hashtable.h:174:7: note: default constructor of '_Hashtable<std::unordered_multiset<char, std::hash<char>, std::equal_to<char>, std::allocator<char>>, std::pair<const std::unordered_multiset<char, std::hash<char>, std::equal_to<char>, std::allocator<char>>, std::vector<std::__cxx11::basic_string<char>, std::allocator<std::__cxx11::basic_string<char>>>>, std::allocator<std::pair<const std::unordered_multiset<char, std::hash<char>, std::equal_to<char>, std::allocator<char>>, std::vector<std::__cxx11::basic_string<char>, std::allocator<std::__cxx11::basic_string<char>>>>>, std::__detail::_Select1st, std::equal_to<std::unordered_multiset<char, std::hash<char>, std::equal_to<char>, std::allocator<char>>>, std::hash<std::unordered_multiset<char, std::hash<char>, std::equal_to<char>, std::allocator<char>>>, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<true, false, true>>' is implicitly deleted because base class '__detail::_Hashtable_base<unordered_multiset<char, hash<char>, equal_to<char>, allocator<char>>, pair<const unordered_multiset<char, hash<char>, equal_to<char>, allocator<char>>, vector<basic_string<char>, allocator<basic_string<char>>>>, _Select1st, equal_to<unordered_multiset<char, hash<char>, equal_to<char>, allocator<char>>>, hash<unordered_multiset<char, hash<char>, equal_to<char>, allocator<char>>>, _Mod_range_hashing, _Default_ranged_hash, _Hashtable_traits<true, false, true>>' has a deleted default constructor
    : public __detail::_Hashtable_base<_Key, _Value, _ExtractKey, _Equal,
      ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/hashtable_policy.h:1822:5: note: explicitly defaulted function was implicitly deleted here
    _Hashtable_base() = default;
    ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/hashtable_policy.h:1771:5: note: default constructor of '_Hashtable_base<std::unordered_multiset<char, std::hash<char>, std::equal_to<char>, std::allocator<char>>, std::pair<const std::unordered_multiset<char, std::hash<char>, std::equal_to<char>, std::allocator<char>>, std::vector<std::__cxx11::basic_string<char>, std::allocator<std::__cxx11::basic_string<char>>>>, std::__detail::_Select1st, std::equal_to<std::unordered_multiset<char, std::hash<char>, std::equal_to<char>, std::allocator<char>>>, std::hash<std::unordered_multiset<char, std::hash<char>, std::equal_to<char>, std::allocator<char>>>, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Hashtable_traits<true, false, true>>' is implicitly deleted because base class '_Hash_code_base<std::unordered_multiset<char, std::hash<char>, std::equal_to<char>, std::allocator<char>>, std::pair<const std::unordered_multiset<char, std::hash<char>, std::equal_to<char>, std::allocator<char>>, std::vector<std::__cxx11::basic_string<char>, std::allocator<std::__cxx11::basic_string<char>>>>, std::__detail::_Select1st, std::hash<std::unordered_multiset<char, std::hash<char>, std::equal_to<char>, std::allocator<char>>>, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, _Hashtable_traits<true, false, true>::__hash_cached::value>' has a deleted default constructor
  : public _Hash_code_base<_Key, _Value, _ExtractKey, _H1, _H2, _Hash,
    ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/hashtable_policy.h:1373:7: note: explicitly defaulted function was implicitly deleted here
      _Hash_code_base() = default;
      ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/hashtable_policy.h:1349:7: note: default constructor of '_Hash_code_base<std::unordered_multiset<char, std::hash<char>, std::equal_to<char>, std::allocator<char>>, std::pair<const std::unordered_multiset<char, std::hash<char>, std::equal_to<char>, std::allocator<char>>, std::vector<std::__cxx11::basic_string<char>, std::allocator<std::__cxx11::basic_string<char>>>>, std::__detail::_Select1st, std::hash<std::unordered_multiset<char, std::hash<char>, std::equal_to<char>, std::allocator<char>>>, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, true>' is implicitly deleted because base class '_Hashtable_ebo_helper<1, std::hash<std::unordered_multiset<char, std::hash<char>, std::equal_to<char>, std::allocator<char>>>>' has a deleted default constructor
      private _Hashtable_ebo_helper<1, _H1>,
      ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/hashtable_policy.h:1096:7: note: explicitly defaulted function was implicitly deleted here
      _Hashtable_ebo_helper() = default;
      ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/hashtable_policy.h:1094:7: note: default constructor of '_Hashtable_ebo_helper<1, std::hash<std::unordered_multiset<char, std::hash<char>, std::equal_to<char>, std::allocator<char>>>, true>' is implicitly deleted because base class 'std::hash<std::unordered_multiset<char, std::hash<char>, std::equal_to<char>, std::allocator<char>>>' has a deleted default constructor
    : private _Tp
      ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/functional_hash.h:101:19: note: default constructor of 'hash<std::unordered_multiset<char, std::hash<char>, std::equal_to<char>, std::allocator<char>>>' is implicitly deleted because base class '__hash_enum<std::unordered_multiset<char, std::hash<char>, std::equal_to<char>, std::allocator<char>>>' has no default constructor
    struct hash : __hash_enum<_Tp>
                  ^

Answer 1

不能将unordered_multiset原样用作unordered_map中的键，因为它没有std::hash专门化。

您可以专门化std::hash或为unordered_multiset提供自己的哈希函数。

但这些实际上都不需要，因为您可以使用排序的字符串作为键：

vector<vector<string>> groupAnagrams(vector<string> &strs)
{
    map <string, vector<string>> mp1;
    for (auto &s : strs) {
        string sc = s;
        sort(begin(sc), end(sc));
        mp1[sc].push_back(s);
    }
    vector<vector<string>> res;
    for (auto &c : mp1) {
        res.push_back(c.second);
    }
    return res;
}

Answer 2

unordered_map要求密钥类型有一个哈希函数。在本例中，它是unordered_multiset ，但没有unordered_multiset 的std::hash专门化。您将需要制作您自己的收割机，以便使用这个。

这里的错误信息并不是最大的，但这是暗指的。