Good hash function over C++ unordered_set -

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i'm looking implement hash function on c++ std::unordered_set<char>. tried using boost::hash_range:

namespace std { template<> struct hash<unordered_set<char> > size_t operator(const unordered_set<char> &s)( {     return boost::hash_range(begin(s), end(s)) }; }

but realised because set unordered, iteration order isn't stable, , hash function wrong. better options me? guess std::set instead of std::unordered_set, using ordered set because it's easier hash seems ... wrong.

a similar question, albeit in c#, asked here:

hash function on list independant of order of items in it

over there, per gave nice language-independent answer should put on right track. in short, input

x1, …, xn

you should map to

f(x1) op … op f(xn)

where

  • f hash function single elements (integer in case)
  • op commutative operator, such xor or plus

hashing integer may seam pointless @ first, goal make 2 neighboring integers dissimilar each other, when combined op not create same result. e.g. if use + operator, want f(1)+f(2) give different result f(0)+f(3).

if standard hashing functions not candidates f , cannot find one, check linked answer more details...


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