Get random not repeating value from array - objective-c

Question

I have method called getRandomCar which is executed via NSTimer for 4 seconds. This method have an array like this
NSArray *cars = [NSArray arrayWithObjects:#"Mercedes", #"Opel", #"Ford", #"Mazda", nil];
The idea is when getRandomCar method is called the returned value to be different from the last returned i.e
Mescedes Opel Mercedes Mazda Ford Opel etc..
not
Mercedes Mercedes Mazda Opel Opel etc...
I have tried this but with no luck.
NSString *car = [[NSString alloc]initWithFormat:#"%#",
[carsArray objectAtIndex:arc4random() % [carsArray count]]];
if ([self.tmpCar isEqualToString:car])
{
car = [carsArray lastObject];
}
[self settmpCar:playerName];

Answer 1

Use this:
NSArray *carsArray = [NSArray arrayWithObjects:#"Mercedes", #"Opel", #"Ford", #"Mazda", nil];
NSMutableString *car = [[NSMutableString alloc] init];
NSMutableString *lastCar = [[NSMutableString alloc] init];
[lastCar setString:#"XXX"];
do {
[car setString:[NSString stringWithFormat:#"%#",
[carsArray objectAtIndex:arc4random() % [carsArray count]]]];
}
while ([lastCar isEqualToString:car]);
[lastCar setString:car];

Answer 2

I'd recommend you to remember the index of the last car. And when you generate a random number check if it's equal to the previous and, if so, generate another number. Sample code:
int test;
int lastValue;
for (int a = 0; a < 10; a++) {
test = arc4random() % 10;
if (test == lastValue) {
while (test == lastValue) {
test = arc4random();
NSLog(#"in While loop");
}
} else {
NSLog(#"%i", test);
}
lastValue = test;
}
Hope it helps
edit
Decided to add the code for you:
NSArray *cars = [NSArray arrayWithObjects:#"Mercedes", #"Opel", #"Ford", #"Mazda", nil];
int test;
int lastValue;
for (int a = 0; a < 20; a++) {
test = arc4random() % [cars count];
if (test == lastValue) {
while (test == lastValue) {
test = arc4random();
}
} else {
NSString *car = [cars objectAtIndex:test];
lastValue = test;
}
}
that will make 20 random non-repeatable cars

Answer 3

You can use another array to hold the cars that have already been picked up before. In the following example, once you exhaust the entire carsArray, method GetCar will return nil. Note that this may not be the most efficient way, but for a small size of carsArray it should work fine.
At the class level:
NSMutableArray *prevCars = [[NSMutableArray alloc] init];
Your method:
-(NSString*) GetCar {
if([prevCars count] == [carsArray count])
return nil;
NSMutableString *car = [[NSMutableString alloc] init];
do {
[car setString:[NSString stringWithFormat:#"%#",
[carsArray objectAtIndex:arc4random() % [carsArray count]]]];
}
while ([InArray:prevCars value:car])
[prevCars addObject:car];
return car;
}
And then:
-(BOOL)InArray:(NSArray *)arr value:(NSString *)val {
for (id Elem in arr) {
if([val isEqualToString:(NSString*)val])
return YES;
}
return NO;
}
Of course, make sure to free the memory when you're done.