Random playlist algorithm

Question

I need to create a list of numbers from a range (for example from x to y) in a random order so that every order has an equal chance.

I need this for a music player I

Answer 1

If memory was really a concern after a certain number of records and it's safe to say that if that memory boundary is reached, there's enough items in the list to not matter if there are some repeats, just as long as the same song was not repeated twice, I would use a combination method.

Case 1: If count < max memory constraint, generate the playlist ahead of time and use Knuth shuffle (see Jon Skeet's implementation, mentioned in other answers).

Case 2: If count >= max memory constraint, the song to be played will be determined at run time (I'd do it as soon as the song starts playing so the next song is already generated by the time the current song ends). Save the last [max memory constraint, or some token value] number of songs played, generate a random number (R) between 1 and song count, and if R = one of X last songs played, generate a new R until it is not in the list. Play that song.

Your max memory constraints will always be upheld, although performance can suffer in case 2 if you've played a lot of songs/get repeat random numbers frequently by chance.