面试题实战

图1.jpeg

面试题如图，解决方案1：

@interface ViewController () {
    int count;
}

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    count = 0;
    int n1 = arc4random()%10000;
    int n2 = arc4random()%10000;
    //要求func1循环n1次，func2循环n2次，并且必须并行运行，然后输出func3的结果
    //如果只用下面这一个多线程方法，加分
//    dispatch_async(dispatch_get_global_queue(0, 0), ^{
//
//    })
    dispatch_group_t group = dispatch_group_create();
    dispatch_queue_t queue = dispatch_get_global_queue(0, 0);

    dispatch_group_async(group, queue, ^{
       
        for (int i = 0; i <n1; i ++) {
            [self func1];
            NSLog(@"func1");
        }
    });
    dispatch_group_async(group, queue, ^{
        
        for (int i = 0; i <n2; i ++) {
            [self func2];
            NSLog(@"func2");
        }
    });
    for (int i = 0; i <n2; i ++) {
         [self func1];
        [self func2];
        NSLog(@"func2");
    }
    dispatch_group_notify(group, queue, ^{
        [self func3];
    });

    
}
- (void)func1 {
    count ++;
}
- (void)func2 {
    count --;
}
- (void)func3 {
    NSLog(@"%d",count);
}

如果只用一个异步操作的话，也有一种方法，用信号量机制，如下图： 图2.jpg