How are popular ranking algorithms such as Reddit and Hacker News working?

Have you ever wondered how people arrange posts on the homepage, the “hot” section of news sites such as Reddit, Hacker News, entertainment sites such as the trending section of Youtube, 9GaG, and Comedy Ignoring, Does anyone know, …

Please do not think about personalizing the content for each user or applying machine learning to the ranking soon. In this article, I would like to analyze the calculation, ranking the articles are “hot” using the simple calculation algorithm, the purest.

Overview

First of all, you need to determine what is the peculiarity of your system/website, how to rank the articles on the home page:

If your system provides knowledge and answers like Quora, Stack Overflow: you need to prioritize providing the most useful information to users first, old or new content is less important. Quora and StackOverFlow both rank the highest upvote — downvote answers on the top. Ranking by “hot” will not be very useful in this case.
If your system is a form of news and entertainment social network: on the homepage, you will need to provide fresh and interesting information to the masses, restricting old and boring information. So you need a ranking algorithm format to sort the article properly. This is the part I will focus on…