iOS: How do I generate 8 unique random integers?

Question

I need to generate 8 random integers, but they need to be unique, aka not repeated.

For example, I want 8 numbers within the range 1 to 8.

I\'ve seen arc4ran

Answer 1

Checking for already generated numbers is potentially expensive (theoretically, it could take forever.) However, this is a solved problem. You want a shuffling algorithm, like the Fisher-Yates_shuffle

On iOS probably something like:

NSMutableArray *randSequence = [[NSMutableArray alloc] initWithCapacity:8];
for (int ii = 1; ii < 9; ++ii)
    [randSequence addObject:[NSNumber numberWithInt:ii]];

for (int ii = 8; ii > 0; --ii) {
    int r = arc4random() % (ii + 1);
    [randSequence exchangeObjectAtIndex:ii withObjectAtIndex:r];

// you can now iterate over the numbers in `randSequence` to get
// your sequence in random order