Final array after merging

After completing the main merge loop, it is necessary to add the remaining elements of one of the vectors to the final array, avoiding additional checks.

std::vector<int> merged{};
merged.reserve(first.size() + second.size());

size_t i = 0, j = 0;
while (i < first.size() && j < second.size()) {
    if (first[i] > second[j]) {
        merged.push_back(second[j++]);
    } else {
        merged.push_back(first[i++]);
    }
}