xcode newArray shuffle

iOS学习笔记——随机打乱一个数组

  
@interface NSMutableArray (ArchUtils_Shuffle)
- (void)shuffle;
@end

// Chooses a random integer below n without bias.
// Computes m, a power of two slightly above n, and takes random() modulo m,
// then throws away the random number if it's between n and m.
// (More naive techniques, like taking random() modulo n, introduce a bias 
// towards smaller numbers in the range.)
static NSUInteger random_below(NSUInteger n) {
    NSUInteger m = 1;
 
    // Compute smallest power of two greater than n.
    // There's probably a faster solution than this loop, but bit-twiddling
    // isn't my specialty.
    do {
        m <<= 1;
    } while(m < n);
 
    NSUInteger ret;
 
    do {
        ret = arc4random() % m;
    } while(ret >= n);
 
    return ret;
}

@implementation NSMutableArray (ArchUtils_Shuffle)

- (void)shuffle {
    // http://en.wikipedia.org/wiki/Knuth_shuffle
 
    for(NSUInteger i = [self count]; i > 1; i--) {
        NSUInteger j = random_below(i);
        [self exchangeObjectAtIndex:i-1 withObjectAtIndex:j];
    }
}

@end

@implementation Practice

- (void) newArrayShuffle
{
 [btn shuffle];
}
@end