02. Odd Occurrences

#include <iostream>
#include <climits>
#include <stack>
#include <string>
#include <vector>
#include <sstream>
#include <list>
#include <algorithm>
using namespace std;

char tolower_char(char c)
{
  return tolower(c);
}

int main()
{
  string buffer;
  getline(cin, buffer);

  istringstream istr(buffer);

  string word;
  list< pair<string, size_t> > words;
  while(istr >> word)
    {
      transform(word.begin(), word.end(), word.begin(), tolower_char);
      bool found = false;
      for(auto & elem : words)
        {
          if(elem.first == word)
          {
          elem.second++;
          found = true;
          break;
        }
    }
  if(!found)
    words.push_back( pair<string, size_t>(word, 1) );
    }
  bool firstWord = true;
  for(auto item : words)
    {
      if(item.second %2 )
      {
        if(!firstWord)
          cout << ", ";
            else
          firstWord = false;
          cout << item.first;
      }
    }
  return 0;
}