2. Odd Occurrences

#include <iostream>
#include <utility>
#include <map>
#include <sstream>
#include <vector>
#include <queue>

using namespace std;

void makeItLowerCases(string& input)
{
    if (input[0] >= '0' && input[0] <= '9')
    {
        input = input;
    }
    else
    {
        const int size = input.size();
        for (int i = 0; i < size; i++)
        {
            if (input[i] >= 'A' && input[i] <= 'Z')
            {
                input[i] = input[i] + 32;
            }
        }
    }
}

int main()
{
    string input;
    getline(cin, input);
    istringstream istr(input);

    string word;

    map<string, int> words;
    queue<string> output;
    vector<string> result;
    while (istr >> word)
    {
        makeItLowerCases(word);

        if (words.find(word) == words.end())
        {
            output.push(word);
        }
        words[word]++;
    }

    while (!output.empty())
    {
        string key = output.front();
        if ((words.find(key)->second % 2) != 0)
        {
            result.push_back(key);
        }
        output.pop();
    }
    int counter = 0;
    const int size = result.size();
    for(string elem : result)
    {
        counter++;
        cout << elem;
        if (counter < size)
        {
            cout << ", ";
        }
    }

    return 0;
}