Free study materials can be found in official website. Click on the Speed School in the upper left corner of official website, and you will see almost all the free materials after entering, as shown in the figure:

Non-free materials were found on the website of Baizhan programmers, including artificial intelligence (359 episodes), Python(900 episodes), JAVA( 1 103 episodes), big data (660 episodes), Internet architecture (300 episodes), soft power in the workplace (292 episodes) and C language (/.