LEAPS = Long-term Equity Anticipation Securities，长期股票期权
到期时间长：>= 1 年，常见 2-3 年
我的最爱：回报高、风险可控、出场灵活
比 Covered Call 更赚钱，也更安心
LEAPS = 期权中的玄铁重剑
录制当天股价 = $170.29
买 100 股 = $170.29 x 100 = $17,029
买 LEAPS = $47.82 x 100 = $4,782
节省资金 = $12,247
Delta ~= 0.75 -> 股价涨 $1，期权涨 $0.75 ~= 持有 75 股
期权总价 = $4,782
内在价值 = ($170.29 - $145) x 100 = $2,529
外在价值 = $4,782 - $2,529 = $2,253
In this chapter, you are asked to design a news feed system. What is news feed? According to the Facebook help page, “News feed is the constantly updating list of stories in the middle of your home page. News Feed includes status updates, photos, videos, links, app activity, and likes from people, pages, and groups that you follow on Facebook” [1]. This is a popular interview question. Similar questions commonly asked are to: Design Facebook news feed, Instagram feed, Twitter timeline, etc.
A notification system has already become a very popular feature for many applications in recent years. A notification alerts a user with important information like breaking news, product updates, events, offerings, etc. It has become an indispensable part of our daily life. In this chapter, you are asked to design a notification system.
A notification is more than just mobile push notification. Three types of notification formats are: mobile push notification, SMS message, and Email. Figure 1 shows an example of each of these notifications.
In this chapter, we focus on web crawler design—an interesting and classic system design interview question.
A web crawler is known as a robot or spider. It is widely used by search engines to discover new or updated content on the web. Content can be a web page, an image, a video, a PDF file, etc. A web crawler starts by collecting a few web pages and then follows links on those pages to collect new content. Figure 1 shows a visual example of the crawl process.
In this chapter, we will tackle an interesting and classic system design interview question: Designing a URL shortening service like TinyURL.
System design interview questions are intentionally left open-ended. To design a well-crafted system, it is critical to ask clarification questions.
Candidate: Can you give an example of how a URL shortener work?
Interviewer: Assume https://www.systeminterview.com/q=chatsystem&c=loggedin&v=v3&l=long is the original URL. Your service creates an alias with shorter length: https://tinyurl.com/y7keocwj. If you click the alias, it redirects you to the original URL.
C: What is the traffic volume?
I: 100 million URLs are generated per day.
C: How long is the shortened URL?
I: As short as possible.
C: What characters are allowed in the shortened URL?
I: Shortened URL can be a combination of numbers (0-9) and characters (a-z, A-Z).
C: Can shortened URLs be deleted or updated?
I: For simplicity, let us assume shortened URLs cannot be deleted or updated.
Here are the basic use cases: