2. Garbage Sorting

#include <iostream>
#include <string>
#include <sstream>
#include <list>

using namespace std;

void showlist(list <int> out)
{
    list<int>::iterator it;
    for (it = out.begin(); it != out.end(); ++it)
    {
        cout << *it << ' ';
    }
}

int main()
{
    int numberOfCommands;
    cin >> numberOfCommands;
    cin.ignore();

    list<int> glass, metal, plastic;
    for (int i = 1; i <= numberOfCommands; i++)
    {
        string input;
        getline(cin, input);
        istringstream istr(input);
        string line, command;
        istr >> line >> command;

        if (line == "glass")
        {
            if (command == "front")
            {
                glass.push_front(i);
            }
            else
            {
                glass.push_back(i);
            }
        }
        else if (line == "metal")
        {
            if (command == "front")
            {
                metal.push_front(i);
            }
            else
            {
                metal.push_back(i);
            }
        }
        else if (line == "plastic")
        {
            if (command == "front")
            {
                plastic.push_front(i);
            }
            else
            {
                plastic.push_back(i);
            }
        }
        else
        {
            i -= 1;
            --numberOfCommands;
        }
    }
    if (!glass.empty())
    {
        cout << "glass - ";
        showlist(glass);
        cout << endl;
    }
    if (!metal.empty())
    {
        cout << "metal - ";
        showlist(metal);
        cout << endl;
    }
    if (!plastic.empty())
    {
        cout << "plastic - ";
        showlist(plastic);
        cout << endl;
    }
    return 0;
}