The first time I read it I didn't know how to solve it, first I tried to solve it with only lists, after a while I realized it was more difficult, I had to learn about dictionaries and a little about graphs, it took me like half a week to succeed before test 9, and an afternoon to understand and make a plan and code the lines that I need to pass that test. Now, after I completed it, I'm the happiest man on earth.