Generates a set of unique random numbers. Useful when you want to pick multiple random elements without duplicates.

RandomNumberGenerator.m

- (NSArray *)generate:(int)n randomUniqueNumbersBetween:(int)lowerLimit upperLimit:(int)upperLimit
{
    NSMutableArray *randomNumberArray = [NSMutableArray arrayWithCapacity:upperLimit-lowerLimit];
    
    // add all numbers to array
    for (int i = lowerLimit; i < upperLimit; i++)
    {
        [randomNumberArray addObject:@(i)];
    }
    
    // shuffle array
    for (NSUInteger i = 0; i < [randomNumberArray count]; i++)
    {
        int j = arc4random_uniform([randomNumberArray count]);
        
        NSNumber *jNumber = randomNumberArray[j];
        NSNumber *iNumber = randomNumberArray[i];
        
        randomNumberArray[j] = iNumber;
        randomNumberArray[i] = jNumber;
    }
    
    return [randomNumberArray subarrayWithRange:NSMakeRange(0,n)];
}