🟡 Port problem 12 (Integer to Roman) from Clojure/Swift to C++23

solutions/0001-0100/0012-integer-to-roman/README.md

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+# 12. Integer to Roman
+
+[LeetCode problem 12](https://leetcode.com/problems/integer-to-roman/)
+
+- **Difficulty**: Medium
+- **Tags**: hash-table, math, string, greedy
+
+## Description
+
+Given an integer in the range `[1, 3999]`, convert it to a Roman numeral,
+handling the six subtractive pairs (`IV`, `IX`, `XL`, `XC`, `CD`, `CM`) that
+Roman numerals use in place of four repeated symbols in a row.

solutions/0001-0100/0012-integer-to-roman/solution.cpp

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+#include "solution.hpp"
+
+#include <array>
+#include <utility>
+
+namespace leetcode::p0012 {
+
+std::string solve(int num) {
+    static constexpr std::array<std::pair<int, const char*>, 13> romanSymbols{{
+        {1000, "M"},
+        {900, "CM"},
+        {500, "D"},
+        {400, "CD"},
+        {100, "C"},
+        {90, "XC"},
+        {50, "L"},
+        {40, "XL"},
+        {10, "X"},
+        {9, "IX"},
+        {5, "V"},
+        {4, "IV"},
+        {1, "I"},
+    }};
+
+    std::string result;
+
+    for (const auto& [value, symbol] : romanSymbols) {
+        while (num >= value) {
+            result += symbol;
+            num -= value;
+        }
+    }
+
+    return result;
+}
+
+} // namespace leetcode::p0012

solutions/0001-0100/0012-integer-to-roman/solution.hpp

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+#pragma once
+
+#include <string>
+
+namespace leetcode::p0012 {
+
+// optimized: O(1) time (13 fixed symbols), O(1) space — greedy, largest
+// symbol first.
+std::string solve(int num);
+
+} // namespace leetcode::p0012

solutions/0001-0100/0012-integer-to-roman/test.cpp

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+#include <catch2/catch_test_macros.hpp>
+
+#include "solution.hpp"
+
+TEST_CASE("Problem 12", "[p0012]") {
+    CHECK(leetcode::p0012::solve(1) == "I");
+    CHECK(leetcode::p0012::solve(4) == "IV");
+    CHECK(leetcode::p0012::solve(9) == "IX");
+    CHECK(leetcode::p0012::solve(58) == "LVIII");
+    CHECK(leetcode::p0012::solve(1994) == "MCMXCIV");
+    CHECK(leetcode::p0012::solve(3999) == "MMMCMXCIX");
+}