gistfile1.m

- (ListNode *)next {
    if (_next) {
        ListNode *nextCopy = [[ListNode alloc] init];
        nextCopy.name = _next.name;
        nextCopy.next = _next.next;
        return nextCopy;
    } else {
        return nil;
    }
}

- (NSUInteger)length_unsafe {
    return [[self class] lengthOfListWithHead_unsafe:self count:0];
}
+ (NSUInteger)lengthOfListWithHead_unsafe:(ListNode *)node count:(NSUInteger)count {
    if (!node)
        return count;
    else {
        __unsafe_unretained ListNode *next = node.next;
        return [self lengthOfListWithHead_unsafe:next count:(count + 1)];
    }
}