Want to generate non repeating random numbers

Question

Possible Duplicate:
Generating non-repeating random numbers

Here is my code

NSUInteger count = 10;
for (NSUInteger i = 0; i < count; ++i) {
    NSLog(@"%d",NeedRandomNumberWithoutRepeat);
}

this output should be like 8 7 9 2 1 4 6 3 5 0 Which is random and not repeating numbers

What you want? id total numbers are 10, you need to generate random number 1 to 10, only once? What for 11th time? — Anoop Vaidya, Dec 14 '12 at 13:42
not problem with generate random number, Problem with repeating number — SachinVsSachin, Dec 14 '12 at 13:44
You probably want a "random permutation" of N numbers. http://stackoverflow.com/questions/8554292/generating-non-repeating-random-numbers contains links to algorithms. — Martin R, Dec 14 '12 at 13:53

Roland Keesom · Answer 1 · 2012-12-14T13:58:31.173

1

This should work:

NSUInteger count = 10;

NSMutableArray *array = [[NSMutableArray alloc]init];
for (NSUInteger i = 0; i < count; ++i) {
    [array addObject:[NSNumber numberWithInt:i]];
}

NSMutableArray *copy = [array mutableCopy];
array = [[NSMutableArray alloc]init];
while ([copy count] > 0)
{
    int index = arc4random() % [copy count];
    id objectToMove = [copy objectAtIndex:index];
    [array addObject:objectToMove];
    [copy removeObjectAtIndex:index];
}

edited Dec 14 '12 at 13:58

answered Dec 14 '12 at 13:27

Roland Keesom

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I tried but still number generate with repetation – SachinVsSachin Dec 14 '12 at 13:30
The code I posted gives random numbers that are different every time. – Roland Keesom Dec 14 '12 at 13:32
I tried your code but, number generate like num == 3 and again num == 3 – SachinVsSachin Dec 14 '12 at 13:42
The code is correct, the problem is % count. That puts the arc4random result in a range between 0 and 9 and in this small range you have collisions. Maybe @sachin can explain what he wants to do so we can help him with the problem. – Pierre Dec 14 '12 at 13:45
I have updated my answer. Now you get an array with 10 numbers in random order. – Roland Keesom Dec 14 '12 at 13:59

score 0 · Answer 2 · edited May 23 '17 at 12:22

This answer is modified version from one of my answer in SO.

So, you may find something strange here, you can however use this as your requirement is similar.

int TOTAL_NUMBER=10;
NSMutableArray *alreadyGeneratedNumbers;


- (void)applicationDidFinishLaunching:(NSNotification *)aNotification{
    alreadyGeneratedNumbers=[NSMutableArray new];
}

-(int)generateRandomNumber{
    int low_bound = 0;
    int high_bound = TOTAL_NUMBER;
    int width = high_bound - low_bound;
    int randomNumber = low_bound + arc4random() % width;

    return randomNumber;
}

- (IBAction)button:(id)sender {
    NSMutableArray *shuffle = [[NSMutableArray alloc] initWithCapacity:1];

    BOOL contains=YES;
    while ([shuffle count]<1) {
        NSNumber *generatedNumber=[NSNumber numberWithInt:[self generateRandomNumber]];

        if (![alreadyGeneratedNumbers containsObject:generatedNumber]) {
            [shuffle addObject:generatedNumber];
            contains=NO;
            [alreadyGeneratedNumbers addObject:generatedNumber];
        }
    }

    NSLog(@"shuffle %@",shuffle);
    NSLog(@"Next Batch");

    if ([alreadyGeneratedNumbers count] >= TOTAL_NUMBER) {
        NSLog(@"\nGame over, Want to play once again?");//or similar kind of thing.
        [alreadyGeneratedNumbers removeAllObjects];
    }
}

score -1 · Answer 3 · answered Dec 14 '12 at 13:57

You put the available numbers in an array, and take the index calculated with arc4random() that goes from 0 to the size of the array -1.When a number comes out you take it away from the array:

NSMutableArray* availableNumbers=[NSMutableArray new];
for(NSUInteger i=0; i<10; i++)
{
    [availableNumbers addObject: @(i)];
}
for(NSUInteger i=0; i<10; i++)
{
    NSUInteger index= arc4random()%availableNumbers.count;
    NSNumber* number= availableNumbers[index];
    NSLog(@"%@",number);
    [availableNumbers removeObjectAtIndex: index];
}

PS: At the last iteration is useless to sue arc4random(), since there's only one number inside.

Want to generate non repeating random numbers

3 Answers3