All questions should be solved in the most efficient time possible, unless otherwise specified in the problem.
Hashmaps here: https://github.com/CS196Illinois/Lecture-Notes/blob/master/hashmaps.md
Arrays here: https://github.com/CS196Illinois/Lecture-Notes/blob/master/python_LoopsAndArrays.md
2d Arrays here: https://github.com/CS196Illinois/Lecture-Notes/blob/master/2dArrays.md
Write your own test cases.
Use good style!
As always, ping staff if you find a bug in the homework!