Add explanation, refactor CPP and add Java code for Visits (usaco1230)

[ChuangSheep]

Fix strange indentation of the cpp code; Add some comments and renamed some variables; Add java implementation;

TODO: add explanation

If any of the below doesn't apply to this Pull Request, mark the checkbox as done.

• [x] I have tested my code.
• [x] I have added my solution according to the steps here.
• [x] I have followed the code conventions mentioned here, which include the following:
  • I understand that if it is clear that I have not attempted to follow these guidelines (ex. if I have not used tabs to indent), my PR will be closed.
  • If changes are requested, I will re-request the review after making them.

[stale[bot]]

This pull request has been automatically marked as stale because it has not had recent activity. Please address the requested changes and re-request reviews. Thank you for your contribution!

[SansPapyrus683]

so how's the explanation going

[ChuangSheep]

so how's the explanation going

emm having contests and exams in the past week. Should be finished by this weekend