Uniqifier

#include <algorithm>
#include <vector>
#include <string>
#include <iostream>
#include <fstream>
#include <unordered_map>
#include <unordered_set>

using std::vector;
using std::string;
using std::unordered_map;
using std::unordered_set;

class uniqify {
    unordered_map<char, unordered_set<string>> maps;
    //mutable unsigned long long linecount{ 0 };

public:

    inline bool exists(const char *filename) const noexcept {
        std::ifstream file(filename);
        bool good = file.good();
        return file.close(), good;
    }

    inline bool exists(const string &filename) const noexcept {
        return exists(filename.c_str());
    }

    vector<string> validate(const vector<string> &wordlists) const noexcept {
        vector<string> available(wordlists.size());
        std::copy_if(wordlists.cbegin(), wordlists.cend(), available.begin(), [this](string file) {return exists(file.c_str()); });
        return available;
    }

    void read(const string &filename) noexcept {
        std::ifstream input(filename);
        string line;
        while (std::getline(input, line)) {
            if (line != "") {
                linecount += 1;
                maps[line.c_str()[0]].insert(line);
                //if (!(linecount % 1000000))
                //  std::cout << "Line count: " << linecount << std::endl;
            }
        }
    }

    void read(const vector<string> &wordlists) noexcept{
        for (auto list : wordlists)
            read(list);
    }

    void write(const char *filename) const noexcept {
        std::ofstream fout(filename);
        for (auto m : maps) {
            for (auto s : m.second) {
                fout << s << "\n";
            }
        }
        fout.close();
    }

    void write(const string &filename) const noexcept {
        write(filename.c_str());
    }

    inline void clear() {
        maps.clear();
    }
};

int main(int argc, char **argv) {
    uniqify u;
    vector<string> lists;
    for (auto i = 2; i < argc; ++i)
        lists.push_back(argv[i]);
    lists.swap(u.validate(lists));
    if (!lists.size())
        return std::cout << "No valid wordlists provided.\n", 0;
    u.read(lists);
    u.write(argv[1]);
    return 0;
}