Question

The following string of mine tried to find difference between two strings. But it’s horribly slow as it iterate the length of string:

#include <string> #include <vector> #include <iostream> using namespace std;   int hd(string s1, string s2) {     // hd stands for 'Hamming Distance'     int dif = 0;      for (unsigned i = 0; i < s1.size(); i++ ) {         string b1 = s1.substr(i,1);         string b2 = s2.substr(i,1);          if (b1 != b2) {             dif++;         }     }        return dif; }  int main() {      string string1 = 'AAAAA';     string string2 = 'ATATT';     string string3 = 'AAAAA';      int theHD12 = hd(string1,string2);     cout << theHD12 << endl;      int theHD13 = hd(string1,string3);     cout << theHD13 << endl; } 

Is there a fast alternative to do that? In Perl we can have the following approach:

sub hd {     return ($_[0] ^ $_[1]) =~ tr/\001-\255//; } 

which is much2 faster than iterating the position.

I wonder what’s the equivalent of it in C++?

Answer 1

Fun with the STL:

#include <numeric>    //inner_product #include <functional> //plus, equal_to, not2 #include <string>    #include <stdexcept>  unsigned int  hd(const std::string& s1, const std::string& s2) {     // TODO: What should we do if s1.size() != s2.size()?     if (s1.size() != s2.size()){       throw std::invalid_argument(           'Strings passed to hd() must have the same lenght'       );     }      return std::inner_product(         s1.begin(), s1.end(), s2.begin(),          0, std::plus<unsigned int>(),         std::not2(std::equal_to<std::string::value_type>())     ); }