roman_numerals: working solution

cpp/roman-numerals/roman_numerals.cpp

@@ -0,0 +1,61 @@
+#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;
+}
+
+}

cpp/roman-numerals/roman_numerals.h

@@ -0,0 +1,10 @@
+#pragma once
+
+#include <string>
+
+#define EXERCISM_RUN_ALL_TESTS
+
+namespace roman {
+
+std::string convert(int);
+}