How can I extract random elements from an array while not producing any duplicates.

Question

I am using the rand() function in my iPhone project to generate a random array index. I generate several random indexes and then get the objects from those indexes. However I don't want to get one object more than once so is there a way to say generate a random number within the range of the array count (which I am already doing) excluding previously picked numbers.

i.e. something like this:

int one = rand() % arrayCount
int two = rand() % arrayCount != one

Thanks

Answer 1

Three possibilities:

Shuffling

Shuffle your array and extract the elements in their order.

Remember

Extract a random element and store it into a NSSet. If you extract one the next time check if it's already in the set. (This is linear time.)

Delete

Use a NSMutableArray and remove already extracted elements from the array. If you don't want to modify the original one make a mutable copy.

Which one's the best depends on your needs.