Loopy Robots.cpp

template <class T>
T& operator+=(T& lhs, const T& rhs)
{
    for (typename T::size_type i = 0; i < lhs.size(); ++i)
        lhs[i] += rhs[i];
    return lhs;
}

struct LoopResponse
{
    const bool isLooping;
    const int numCycles;
};

static LoopResponse determineLooping(const std::string& commandSequence)
{
    std::array<int, 2> distanceTraveled;
    const static std::array<std::array<int, 2>, 4> directionModifications = { { { 1, 0 }, { 0, 1 }, { -1, 0 }, { 0, -1 } } };

    int direction = 0;
    const static int maxDirections = 4;
    for (auto const& character : commandSequence)
    {
        switch (character)
        {
        case 'S':
            distanceTraveled += directionModifications[direction];
            break;
        case 'R':
            direction = (direction + 1) % maxDirections;
            break;
        case 'L':
            direction = (direction - 1) % maxDirections;
            break;
        }
    }

    // We loop if we haven't traveled any distance || if we're not facing north
    const bool traveledNoDistance = (distanceTraveled[0] == 0 && distanceTraveled[1] == 0);
    const bool isLooping = traveledNoDistance || direction != 0;
    const int numCycles = [&]()
    {
        if (traveledNoDistance)
            return 1;
        switch (direction)
        {
            // EAST || WEST -> 4 times
        case 1:
        case 3:
            return 4;
            // SOUTH -> 2 times
        case 2:
            return 2;
        }
        // Invalid
        return -1;
    }();

    return{ isLooping, numCycles };
}