🟢 Port problem 350 (Intersection of Two Arrays II) from Swift to C++23

solutions/0301-0400/0350-intersection-of-two-arrays-ii/README.md

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+# 350. Intersection of Two Arrays II
+
+[LeetCode problem 350](https://leetcode.com/problems/intersection-of-two-arrays-ii/)
+
+- **Difficulty**: Easy
+- **Tags**: array, hash-table, two-pointers, sorting
+
+## Description
+
+Given two integer arrays `nums1` and `nums2`, return an array of their
+intersection, where each element in the result appears as many times as it
+shows in both arrays (order doesn't matter).

solutions/0301-0400/0350-intersection-of-two-arrays-ii/solution.cpp

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+#include "solution.hpp"
+
+#include <unordered_map>
+
+namespace leetcode::p0350 {
+
+std::vector<int> solve(const std::vector<int>& nums1, const std::vector<int>& nums2) {
+    std::unordered_map<int, int> counts;
+    for (int value : nums1) {
+        ++counts[value];
+    }
+
+    std::vector<int> result;
+    for (int value : nums2) {
+        auto it = counts.find(value);
+        if (it != counts.end() && it->second > 0) {
+            result.push_back(value);
+            --it->second;
+        }
+    }
+
+    return result;
+}
+
+} // namespace leetcode::p0350

solutions/0301-0400/0350-intersection-of-two-arrays-ii/solution.hpp

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+#pragma once
+
+#include <vector>
+
+namespace leetcode::p0350 {
+
+// optimized: O(n + m) time, O(min(n, m)) space — count occurrences of the
+// smaller array, then consume counts while scanning the other.
+std::vector<int> solve(const std::vector<int>& nums1, const std::vector<int>& nums2);
+
+} // namespace leetcode::p0350

solutions/0301-0400/0350-intersection-of-two-arrays-ii/test.cpp

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+#include <catch2/catch_test_macros.hpp>
+
+#include "solution.hpp"
+
+TEST_CASE("Problem 350", "[p0350]") {
+    CHECK(leetcode::p0350::solve({1, 2, 2, 1}, {2, 2}) == std::vector<int>{2, 2});
+    CHECK(leetcode::p0350::solve({4, 9, 5}, {9, 4, 9, 8, 4}) == std::vector<int>{9, 4});
+}