Iterating over a list in pseudo-random order without storing a shuffled list

Question

In a game, we use a technique called \'colour picking\' to select units.

This means that every visible unit is given a unique colour.

Here is an example of a

Answer 1

I don't really see the problem. As I wrote in the comments, you need only 128K to store a permutation of [0..64K), and you don't need any allocations inside the main loop. Here's a stateful color store in C++11 (in older C++, use a vector or new[]):

class ColorPicker {
    std::array colors;
    uint16_t idx;

  public:
    ColorPicker() : idx(0)
    {
        std::iota(colors.begin(), colors.end(), 0);
        std::random_shuffle(colors.begin(), colors.end());
    }

    uint16_t next_color()
    {
        return colors[idx++];
    }
};

You only need one of these structures. Now, whenever you create a new unit, call next_color on the ColorPicker and store it on the unit as an attribute.

This solution will cycle though the colors. If that's not desired, do a random_shuffle each time the index wraps around to zero.