Tags: js matrix reverse dart 

Rating:

tl;dr:
1. Notice strange function called after winning the game
2. Reverse a bit, dump parameters with debugger
3. Solve set of linear equations to recover flag

Full writeup: https://github.com/p4-team/ctf/tree/master/2019-09-14-realworld-quals/puzzle

Original writeup (https://github.com/p4-team/ctf/tree/master/2019-09-14-realworld-quals/puzzle).