NSCountedSet *set  = [NSCountedSet setWithCapacity:100];
        for (int i = 0; i < 10; i++) {
            int random = arc4random() % (55 - 20 + 1) + 20;
            printf("%d ", random);
            [set addObject:@(random)];
        }
        for (NSNumber *num in set) {
            NSUInteger count = [set countForObject:num];
            if (count > 1) {
                printf("\n");
                printf("%d : %lu\n",[num intValue], count);
            }
        }

有100个数,每个数的取值范围是[20 55], 找出其中的重复的数,重复的次数.