#include "roman_numerals.h"

#include <string>
#include <vector>

namespace roman {

using namespace std;

string convert(int number)
{
    struct digit_t
    {
        int    key;
        string value;
    };

    static const vector<digit_t> digits = {
        {1000, "M" },
        {500,  "D" },
        {100,  "C" },
        {50,   "L" },
        {10,   "X" },
        {5,    "V" },
        {1,    "I" }
    };

    string result;

    auto append_digit = [&](int key, const string &value) -> void {

                            while (number >= key) {

                                result += value;
                                number -= key;
                            }
                        };

    auto iter = digits.cbegin();
    for (; iter != digits.cend(); ++iter) {

        append_digit(iter->key, iter->value);

        auto next_iter = next(iter);

        while (next_iter != digits.cend()
                && 2*next_iter->key >= iter->key) {
            ++next_iter;
        }

        if (next_iter == digits.cend())
            continue;

        append_digit(iter->key - next_iter->key,
                     next_iter->value + iter->value);
    }

    return result;
}

}