Basically, the score is under the structure of a user
So when I migrate a person who already solved the problem in the team to another team
Then the score will be double for questions.
Since the the limitation of each team is 5 users maximum, which can gives us 5 times of the original score.

Create Account A, Account B.
A: Create Team α.
B: Create Team β.
A, B solved a question which is 100 points.
B remove himself from the β, which also delete the team.
B join the α. Now, Team α has two people who already solved the question, so the team got 100+100 points.

I created 5 users, and created 5 team for each user.

Then let 5 users join the same team, the status of problem became

I solved some questions for each users, which gives me total 4500 points.

1. Remove all submission after users leave a team
2. Check repeat submission, and remove them before a user join a new team

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