🟢 Port problem 1929 (Concatenation of Array) from Swift to C++23

solutions/1901-2000/1929-concatenation-of-array/README.md

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+# 1929. Concatenation of Array
+
+[LeetCode problem 1929](https://leetcode.com/problems/concatenation-of-array/)
+
+- **Difficulty**: Easy
+- **Tags**: array, simulation
+
+## Description
+
+Given an integer array `nums` of length `n`, return an array `ans` of length
+`2n` where `ans[i] == nums[i]` and `ans[i + n] == nums[i]` for `0 <= i < n`
+(i.e. `nums` concatenated with itself).

solutions/1901-2000/1929-concatenation-of-array/solution.cpp

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+#include "solution.hpp"
+
+namespace leetcode::p1929 {
+
+std::vector<int> solve(const std::vector<int>& nums) {
+    std::vector<int> result;
+    result.reserve(nums.size() * 2);
+    result.insert(result.end(), nums.begin(), nums.end());
+    result.insert(result.end(), nums.begin(), nums.end());
+    return result;
+}
+
+} // namespace leetcode::p1929

solutions/1901-2000/1929-concatenation-of-array/solution.hpp

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+#pragma once
+
+#include <vector>
+
+namespace leetcode::p1929 {
+
+// optimized: O(n) time, O(n) space — append nums to a copy of itself.
+std::vector<int> solve(const std::vector<int>& nums);
+
+} // namespace leetcode::p1929

solutions/1901-2000/1929-concatenation-of-array/test.cpp

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+#include <catch2/catch_test_macros.hpp>
+
+#include "solution.hpp"
+
+TEST_CASE("Problem 1929", "[p1929]") {
+    CHECK(leetcode::p1929::solve({1, 2, 1}) == std::vector<int>{1, 2, 1, 1, 2, 1});
+    CHECK(leetcode::p1929::solve({1, 3, 2, 1}) == std::vector<int>{1, 3, 2, 1, 1, 3, 2, 1});
+}