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 arc4random but I'm not sure how to make them unique ?
Solution
-(NSMutableArray *)getRandomInts:(int)amount from:(int)fromInt to:(int)toInt {
if ((toInt - fromInt) +1 < amount) {
return nil;
}
NSMutableArray *uniqueNumbers = [[[NSMutableArray alloc] init] autorelease];
int r;
while ([uniqueNumbers count] < amount) {
r = (arc4random() % toInt) + fromInt;
if (![uniqueNumbers containsObject:[NSNumber numberWithInt:r]]) {
[uniqueNumbers addObject:[NSNumber numberWithInt:r]];
}
}
return uniqueNumbers;
}
-(NSMutableArray *)getEightRandom {
NSMutableArray *uniqueNumbers = [[[NSMutableArray alloc] init] autorelease];
int r;
while ([uniqueNumbers count] < 8) {
r = arc4random();
if (![uniqueNumbers containsObject:[NSNumber numberWithInt:r]]) {
[uniqueNumbers addObject:[NSNumber numberWithInt:r]];
}
}
return uniqueNumbers;
}
If you want to restrict to numbers less than some threshold M, then you can do this by:
-(NSMutableArray *)getEightRandomLessThan:(int)M {
NSMutableArray *uniqueNumbers = [[[NSMutableArray alloc] init] autorelease];
int r;
while ([uniqueNumbers count] < 8) {
r = arc4random() % M; // ADD 1 TO GET NUMBERS BETWEEN 1 AND M RATHER THAN 0 and M-1
if (![uniqueNumbers containsObject:[NSNumber numberWithInt:r]]) {
[uniqueNumbers addObject:[NSNumber numberWithInt:r]];
}
}
return uniqueNumbers;
}
If M=8, or even if M is close to 8 (e.g. 9 or 10), then this takes a while and you can be more clever.
-(NSMutableArray *)getEightRandomLessThan:(int)M {
NSMutableArray *listOfNumbers = [[NSMutableArray alloc] init];
for (int i=0 ; i<M ; ++i) {
[listOfNumbers addObject:[NSNumber numberWithInt:i]]; // ADD 1 TO GET NUMBERS BETWEEN 1 AND M RATHER THAN 0 and M-1
}
NSMutableArray *uniqueNumbers = [[[NSMutableArray alloc] init] autorelease];
int r;
while ([uniqueNumbers count] < 8) {
r = arc4random() % [listOfNumbers count];
if (![uniqueNumbers containsObject:[listOfNumbers objectAtIndex:r]]) {
[uniqueNumbers addObject:[listOfNumbers objectAtIndex:r]];
}
}
[listOfNumbers release];
return uniqueNumbers;
}