How can I browse some document-like apps offline? Some Android apps are actually some kind of documents/ebooks, but it seems that I can't browse it offline. for example, it seems that when my phone is not connected to a network or mobile data service, the following app doesn't load


LeetCode Cracker 


How can I browse such apps offline?

Thanks.
The app doesn't save anything, and it's using in-app browser to load the codes from GitHub repository. From its app description,

All of my solution files are on GitHub, and are in Java. It contains almost all of the problems of LeetCode except some of them I haven't came up with a good solution. Since this app read files from GitHub repository, it requires network connection. I think this will not require too much data usage. And it make it easy for me to update solutions without update this app.
(Emphasis mine)

Searching based on it returned the corresponding GitHub repository.
Now, given the GitHub repository, the next step is to clone it to the device (e.g. for offline usage). As of current, I only found and tested SGit, and it worked for me.
Usage:

Install and open SGit
Tap Clone (plus icon) on the top bar
For Remote URL, input https://github.com/softstar1990/LeetCode.
For Local Path, input anything that can be used as identifier (e.g. LeetCode).
Tap Clone. The cloned repository will be stored on: [sdcard dir]/Android/data/me.sheimi.sgit/files/repo/[Local Path]
Browse the repository from SGit offline.