feat: add C++ Two Sum solution

solutions/cpp/practice1.cpp

@@ -0,0 +1,36 @@
+// Problem: Two Sum
+// Source: https://leetcode.com/problems/two-sum/
+// Note: Uses an unordered_map for efficient O(n) lookup.
+
+#include <iostream>
+#include <vector>
+#include <unordered_map>
+using namespace std;
+
+vector<int> twoSum(const vector<int>& nums, int target) {
+    unordered_map<int, int> seen;
+
+    for (int i = 0; i < static_cast<int>(nums.size()); i++) {
+        int complement = target - nums[i];
+
+        if (seen.find(complement) != seen.end()) {
+            return {seen[complement], i};
+        }
+
+        seen[nums[i]] = i;
+    }
+
+    return {};
+}
+
+int main() {
+    vector<int> result1 = twoSum({2, 7, 11, 15}, 9);
+    vector<int> result2 = twoSum({3, 2, 4}, 6);
+    vector<int> result3 = twoSum({3, 3}, 6);
+
+    for (const auto& result : {result1, result2, result3}) {
+        cout << "[" << result[0] << ", " << result[1] << "]" << endl;
+    }
+
+    return 0;
+}