Challenge 2

Find and fix the problem.

#import "XYZAppDelegate.h"

@interface XYZParent : NSObject

@property (atomic) NSMutableArray *children;

@end

@implementation XYZParent
@end

@interface XYZChild : NSObject

@property (atomic) XYZParent *parent;

@end

@implementation XYZChild
@end

@implementation XYZAppDelegate

- (BOOL)application:(UIApplication *)application
  didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    XYZParent *parent = [[XYZParent alloc] init];
    parent.children = [[NSMutableArray alloc] init];
    for (int i = 0; i < 10; i++) {
        XYZChild *child = [[XYZChild alloc] init];
        child.parent = parent;
        [parent.children addObject:child];
    }
    return YES;
}
@end