I'm trying to write a way to generate a random array of X
numbers, and
the numbers need to be between 0 and X, and not be repeating (its
for
generating a random playlist.)
Just generate the random playlist directly, don't bother with
indexes.
Put the tracks into an array, then use the canonical shuffle
algorithm
which, in pseudocode, is:
for i from 0 to array_length - 2
random_index = random in [i, array_length - 1]
swap array[i] with array[random_index]
Transforming this into real code is left as an exercise for the
reader.
@implementation NSMutableArray (Shuffling)
- (void)shuffle
{
int max = [self count] -1;
random() % max returns 0 through (max -1), so you're never going to
get a random value for the last array position. This line should be:
int max = [self count];
int i;
for (i = 0; i < max; i++) {
int choice = random() % max;
You actually need to pick a random number between i (inclusive) and
max, so this line would be
int choice = i + (random() % (max - i ));
Also, the last time through the loop, the last array element can only
exchange places with itself, so as an optimization you would write the
for loop as:
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