Random number that doesn't repeat twice in a row [duplicate] - ios

Question

This question already has answers here:
Non repeating random numbers in Objective-C
(6 answers)
Closed 7 years ago.
I'm pretty new to coding, I've been looking for similar questions but none fits my needs. I'm working in a dice rolling app, and I need a a random number generator to "roll" the dice. arc4random seems perfect, but the problems that I can't have the same face occurring twice in a row. I have a method firing when I press the button with a timer
- (IBAction)dieRoll:(id)sender {
self.currentFace = 1;
_timer = [NSTimer scheduledTimerWithTimeInterval:0.25 target:self selector:#selector(roll) userInfo:nil repeats:YES];;
}
but I have to implement the 'roll' method where I get a random number different from the one already selected (the property self.currentFace).
any clue?

Answer 1

this is how your implementation could look like:
#interface ViewController ()
#property (assign, nonatomic) NSInteger currentFace;
#end
#implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
self.currentFace = -1;
}
- (IBAction)diceRoll:(id)sender {
NSInteger newFace = -1;
do {
newFace = arc4random_uniform(6) + 1;
} while (newFace == self.currentFace);
self.currentFace = newFace;
}
#end

Answer 2

A simple solution would be to just remember the last rolled number and roll the dice until you get a different one. Pretty simple and you can keep arc4random.
An example:
- (NSUInteger)rollDiceWithLastFaceNumber:(NSUInteger)lastFaceNumber
{
NSUInteger currentFaceNumber;
do {
currentFaceNumber = (arc4random_uniform(6) + 1);
} while (currentFaceNumber == lastFaceNumber);
return currentFaceNumber;
}
and how to use it:
[self rollDiceWithLastFaceNumber:3];

Answer 3

This solution avoids an unknown number of iterations until you get your result.
- (void)roll {
NSUInteger next = [self nextFaceWithPreviousFace:self.currentFace];
NSLog(#"%lu", next);
self.currentFace = next;
}
- (NSUInteger)nextFaceWithPreviousFace:(NSUInteger)previous {
NSMutableArray *candidates = [NSMutableArray arrayWithObjects:#1, #2, #3, #4, #5, #6, nil];
[candidates removeObject:#(previous)];
NSUInteger index = arc4random_uniform((unsigned)candidates.count);
return [candidates[index] unsignedIntegerValue];
}